General pharmacological effects of N2-[(N-acetyl-muramoyl)-L-alanyl-D-isoglutaminyl]-N6-stearoyl-L-ly sine MDP-Lys(L18), muroctasin) were examined and the following results were obtained. 1. Central nervous system: MDP-Lys(L18) had no effect on behavior, spontaneous motor activity, electroshock- and chemoshock-induced convulsions, hexobarbital sleeping time, pain threshold (mice), conditioned avoidance response (rats) at a dose of 0.4 mg/kg, s.c. and EEG as well as spinal reflex (cats) at a dose of 0.4 mg/kg, i.v. It produced a significant elevation in body temperature (rabbits) at doses of 13 micrograms/kg, s.c. and greater. 2. Respiratory and cardiovascular system (dogs): MDP-Lys(L18) did not show any significant effect on respiratory and cardiovascular functions at a dose of 0.4 mg/kg i.v. 3. Autonomic nervous system: MDP-Lys(L18) induced a miosis (rabbits) at doses of 13 micrograms/kg s.c. and greater. It did not affect norepinephrine-induced pressor and acetylcholine-induced depressor responses (dogs) and contraction of the nictitating membrane induced by electrical stimulation (cats) at a dose of 0.4 mg/kg i.v. 4. Smooth muscles: In the experiments using the isolated ileum, vas deferens, trachea (guinea pigs) and uterus (rats), MDP-Lys(L18) showed neither spasmogenic nor spasmolytic activity at a concentration of 4 x 10(-6) g/ml. Gastrointestinal propulsion (mice), gastric mucosa, gastric emptying rate and gastric secretion (rats) were not affected by this drug at a dose of 0.4 mg/kg s.c. MDP-Lys(L18) did not influence gastrointestinal motility (dogs) at a dose of 0.4 mg/kg, i.v. 5. Miscellaneous: MDP(L-18) suppressed carrageenan-induced edema (rats) at doses of 0.13 mg/kg s.c. and greater.(ABSTRACT TRUNCATED AT 250 WORDS)