diff --git a/Makefile b/Makefile
index df473ef..3a51ce3 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 CFLAGS=-Wall -g -pthread
 LDFLAGS=-pthread
 
-OBJS=main.o map.o agent.o connection.o
+OBJS=main.o map.o agent.o connection.o pheromone.o
 
 brmlife: $(OBJS)
 	$(CXX) $(LDFLAGS) -o $@ $^
diff --git a/agent.cc b/agent.cc
index 61fcef8..fefe291 100644
--- a/agent.cc
+++ b/agent.cc
@@ -91,6 +91,15 @@ agent::attack_dir(int dir_x, int dir_y)
 	return attack_roll >= defense_roll;
 }
 
+bool
+agent::secrete(int id, double intensity)
+{
+	pheromone p(id, intensity);
+	pheromones.secrete(p);
+	chenergy(intensity * world::pheromone_cost);
+	return true;
+}
+
 void
 agent::chenergy(int delta)
 {
@@ -129,9 +138,13 @@ agent::on_action_takes(void)
 void
 agent::on_tick(void)
 {
+	pheromones.decay(world::phdecay_gamma, world::phdecay_delta);
+
 	if (!tile)
 		return;
 
+	pheromones.seep(tile->pheromones, world::phseep_alpha, world::phseep_beta);
+
 	if (!dead) {
 		chenergy(world::sun_energy);
 		chenergy(attr.move * world::move_idle_cost);
diff --git a/agent.h b/agent.h
index 911a46e..5687d1f 100644
--- a/agent.h
+++ b/agent.h
@@ -2,6 +2,7 @@
 #define BRMLIFE__AGENT_H
 
 #include "map.h"
+#include "pheromone.h"
 #include "world.h"
 
 class connection;
@@ -23,6 +24,8 @@ public:
 	int energy;
 	bool dead;
 
+	class pheromones pheromones;
+
 	agent(int id_, class connection *conn_, class map &map_)
 	: id (id_), conn (conn_), map (map_), tile (NULL)
 	{
@@ -37,6 +40,7 @@ public:
 
 	bool move_dir(int dir_x, int dir_y);
 	bool attack_dir(int dir_x, int dir_y);
+	bool secrete(int id, double intensity);
 
 	void chenergy(int delta);
 	void die(void);
diff --git a/connection.cc b/connection.cc
index 95e3a43..c283e36 100644
--- a/connection.cc
+++ b/connection.cc
@@ -37,6 +37,19 @@ connection::senses(int tick_id, class agent &a)
 	}
 	bufp += snprintf(bufp, sizeof(buf) - (bufp - buf), "\r\n");
 
+	bufp += snprintf(bufp, sizeof(buf) - (bufp - buf), "pheromones");
+	for (int i = 0; i < dir_n; i++) {
+		bufp += snprintf(bufp, sizeof(buf) - (bufp - buf), " (");
+		class pheromones &ps = a.tile->tile_in_dir(dirs[i][0], dirs[i][1]).pheromones;
+		for (std::list<class pheromone>::iterator pi = ps.spectrum.begin(); pi != ps.spectrum.end(); pi++) {
+			if (pi != ps.spectrum.begin())
+				bufp += snprintf(bufp, sizeof(buf) - (bufp - buf), ",");
+			bufp += snprintf(bufp, sizeof(buf) - (bufp - buf), "%d:%f", pi->id, pi->val);
+		}
+		bufp += snprintf(bufp, sizeof(buf) - (bufp - buf), ")");
+	}
+	bufp += snprintf(bufp, sizeof(buf) - (bufp - buf), "\r\n");
+
 	bufp += snprintf(bufp, sizeof(buf) - (bufp - buf), "\r\n");
 	pthread_mutex_lock(&buf_lock);
 	out_buf.append(buf);
@@ -102,6 +115,14 @@ connection::actions(class agent &agent)
 			if (!agent.attack_dir(x, y))
 				bump();
 			mask |= 2;
+		} else if (!negotiation && !cmd.compare("secrete")) {
+			int id = 0; double v = 0;
+			sscanf(line.c_str(), "%d %lf", &id, &v);
+			if (id < 0) id = 0; if (id >= PH_COUNT) id = PH_COUNT - 1;
+			if (v < 0) v = 0;
+			if (!agent.secrete(id, v))
+				bump();
+			/* We deliberately allow multiple secrete commands. */
 
 		} else {
 			std::cout << "unknown line " << cmd << " " << line << " ...\n";
diff --git a/map.cc b/map.cc
index ddfe787..43bfe43 100644
--- a/map.cc
+++ b/map.cc
@@ -39,6 +39,8 @@ tile::on_tick(void)
 		if (tile_in_dir(-1, 0).herb_here()) { tile_in_dir(-1, 0).agent->chenergy(world::soil_energy / herbs); }
 		if (tile_in_dir(0, -1).herb_here()) { tile_in_dir(0, -1).agent->chenergy(world::soil_energy / herbs); }
 	}
+
+	pheromones.decay(world::phdecay_gamma, world::phdecay_delta);
 }
 
 bool
diff --git a/map.h b/map.h
index 9f7027e..b527f2f 100644
--- a/map.h
+++ b/map.h
@@ -1,6 +1,8 @@
 #ifndef BRMLIFE__MAP_H
 #define BRMLIFE__MAP_H
 
+#include "pheromone.h"
+
 class agent;
 class map;
 
@@ -10,6 +12,7 @@ public:
 	class map &map;
 
 	class agent *agent;
+	class pheromones pheromones;
 
 	tile(int x_, int y_, class map &map_)
 	: x(x_), y(y_), map(map_), agent(NULL) {};
diff --git a/pheromone.cc b/pheromone.cc
new file mode 100644
index 0000000..c5c4894
--- /dev/null
+++ b/pheromone.cc
@@ -0,0 +1,48 @@
+#include <cassert>
+#include <cstdlib>
+#include <cmath>
+#include <iostream>
+
+#include "pheromone.h"
+#include "main.h"
+
+
+void
+pheromones::secrete(class pheromone &p)
+{
+	for (std::list<class pheromone>::iterator pi = spectrum.begin(); pi != spectrum.end(); pi++) {
+		if (pi->id < p.id)
+			continue;
+		if (pi->id == p.id) {
+			pi->val += p.val;
+			return;
+		}
+		spectrum.insert(pi, p);
+		return;
+	}
+	spectrum.push_back(p);
+}
+
+void
+pheromones::seep(class pheromones &to, double alpha, double beta)
+{
+	for (std::list<class pheromone>::iterator pi = spectrum.begin(); pi != spectrum.end(); pi++) {
+		class pheromone p(pi->id, pi->val * (alpha * PH_COUNT / pi->id + beta));
+		to.secrete(p);
+	}
+}
+
+void
+pheromones::decay(double gamma, double delta)
+{
+	for (std::list<class pheromone>::iterator pi = spectrum.begin(); pi != spectrum.end(); pi++) {
+next_p:
+		pi->val *= gamma;
+		pi->val -= delta;
+		if (pi->val < 0.001) {
+			pi = spectrum.erase(pi);
+			if (pi != spectrum.end())
+				goto next_p;
+		}
+	}
+}
diff --git a/pheromone.h b/pheromone.h
new file mode 100644
index 0000000..0783a82
--- /dev/null
+++ b/pheromone.h
@@ -0,0 +1,35 @@
+#ifndef BRMLIFE__PHEROMONE_H
+#define BRMLIFE__PHEROMONE_H
+
+/* Pheromone spectrum in a particular state. */
+
+#include <list>
+
+#define PH_COUNT 65536
+
+class pheromone {
+public:
+	int id;
+	double val;
+
+	pheromone(int id_ = 0, double val_ = 0)
+	: id (id_), val (val_) {};
+};
+
+class pheromones {
+public:
+	std::list<class pheromone> spectrum;
+
+	/* Add a pheromone to the spectrum. */
+	void secrete(class pheromone &p);
+	/* Merge slight trail of spectrum to another spectrum (transfer
+	 * by touching). Pheromones with lower index are transmitted
+	 * better than those with higher index:
+	 * v' = v * (alpha / i + beta) */
+	void seep(class pheromones &to, double alpha, double beta);
+	/* Decay the spectrum, multiplying each value by gamma and
+	 * then reducing it by delta. */
+	void decay(double gamma, double delta);
+};
+
+#endif
diff --git a/world.h b/world.h
index 47a3b81..a70ea18 100644
--- a/world.h
+++ b/world.h
@@ -9,6 +9,7 @@ struct world {
 	const static int move_cost = -50;
 	const static int attack_cost = -400;
 	const static int defense_cost = -200;
+	const static int pheromone_cost = -10;
 
 	const static int move_idle_cost = -15; /* ... * attr.move */
 	const static int attack_idle_cost = -15; /* ... * attr.attack */
@@ -21,6 +22,11 @@ struct world {
 	const static int dead_decay = -50;
 
 	const static int herb_rate = 15; /* initially, one herb per herb_rate tiles */
+
+	const static double phseep_alpha = 0.1;
+	const static double phseep_beta = 0.05;
+	const static double phdecay_gamma = 0.95;
+	const static double phdecay_delta = 0.01;
 };
 
 #endif