Effects of two immunosuppressors, cyclophosphane abd 5-fluorouracyl, used in clinical practice for treatment of oncological diseases, were assessed in respect to cytotoxicity and activity of several lysosomal enzymes located in splenocyte granules of C3HA mice. 48 h after a single intraperitoneal injection, both preparations produced a marked decrease in their cytotoxic activity, which was accompanied by a pronounced splenopathy. Both preparations were shown to decrease activity of arylsulfatase. Administration of cyclophosphane brought about the rise of activity of acid lipase as compared to control. Activities of acid phosphatase, alpha-mannosidase, beta-galactosidase, and N-acetyl-beta-D-glucosidase did not change after administration of the used immunosuppressors. It may be suggested that only arylsulfatase and acid lipase are involved in performance and(or) manifestation of the natural killer activity in splenocytes of the C3HA mice after their administration with cyclophosphane or 5-fluorouracyl.