Effects of single and repeated injections of lysosomotropic agent chloroquine on lysosomal proteolytic activity and physico-chemical properties of rat liver lysosomes have been studied. Chloroquine was administered intraperitoneally to rats at a dose of 30 mg/kg of body mass. Osmotic properties, lysosomal enzymes activity and functional state of the system of mononuclear phagocytes were estimated. No alterations of colloid carbon clearance followed by a single dose of chloroquine administration were noted. Distinct alterations in osmotic properties, weak labilization of lysosomes and an increase in acid hydrolases activity were similar after single and/or repeated chloroquine administrations, whereas activation of cysteine proteinases and cathepsin D were most pronounced. Chloroquine accumulation by rat liver cells proved to be similar, but the drug excretion was longer after repeated injections. The lysosomal disorders noted were similar to those symptoms of lysosomal storage disease.