The total catecholamines in the urine of rats collected during 5 h after stimulation of diuresis with 50 ml tap water/kg body weight per os were significantly changed following a 3 wk training in individual metabolic cages, a short pressing of the animals against the laboratory table, a single i.p. injection of 2 ml sodium chloride solution (145 mmol/l)/kg body wt or a single s.c. injection of 40 ml air per animal. The excretion was increased after puncture of the retroorbital plexus and after exposure to cold (+5.degree. C) during the 5 h. Co poisoning produces an inhibition of diuresis. To study the effect of Co intoxications on urinary catecholamine excretion, 25 ml tap water/kg was administered. Single s. c. injection of 7.2 mmol CO/kg body wt (53% COHb) induced a significant increase of urinary catecholamines. Due to repeated injections of the same CO dose, a gradual disappearance of this effect was seen. After 4 wk the differences to controls are negligible.