Exposure of rat's peritoneal macrophages to chlorhexidine at concentrations up to 0.01 per cent resulted in the release of lysosomal enzymes, e.g. chloride-dependent arginine aminopeptidase andβ-D-glucuronidase into the medium from resting cells. The activity of extracellular lactate dehydrogenase increased up to the concentration of 0.01 % and then decreased with increasing chlorhexidine concentration. This could indicate a certain type of»mummifying«of the cells and/or their membranes. The incorporation of trypan blue was found in all cells after a rinse with 0.05 per cent or higher concentrations of chlorhexidine. The direct effect of chlorhexidine on these enzyme activities showed a slight activation ofβ-D-glucuronidase and lactate dehydrogenase, but an inhibition of arginine aminopeptidase. Also the binding of chlorhexidine to cells was found. Low chlorhexidine concentrations caused an additional enzyme release from phagocytizing cells.