Thioglycollate-elicited mouse peritoneal macrophages were cultivated in vitro in control medium or medium containing nicotine (1 nM-1 microM). The drug caused a moderate lysosomal vacuolation and formation of vesicles with a dense core or ring. Furthermore, it partially inhibited uptake and intracellular degradation of horseradish peroxidase without affecting the specific activities of the lysosomal enzymes beta-glucuronidase and beta-N-acetylglucosaminidase in lysates of the cells. A slight inhibitory effect on the phagocytosis of latex beads was also noted. Since nicotine was used in concentrations of the same magnitude that may be obtained in the blood after smoking one cigarette, it seems worthwhile to further explore these findings in relation to the medical risks of smoking.