Abstract. Erythrocyte and lymphocyte NAD + glycohydrolase levels were previously found to be elevated in cancer patients. These results were confirmed in an animal model. The administration of live Ehrlich ascites tumor cells to BALB/c mice led to increases in erythrocyte and lymphocyte NAD + glycohydrolase, along with tumor development. Serum samples, ascites fluid from mice with developed tumors, serum samples from cancer patients and Ehrlich cell supernatants had a similar stimulatory effect when administered to mice or when incubated with peripheric lymphocytes in culture. These increases were accompanied by the appearance of an anti-CD38 reactive band of 45 kDa in SDS-PAGE/Western blot analyses of erythrocyte ghost and lymphocyte membrane proteins. The results, supported by flow cytometry data, support previous clinical findings that an enhancement in CD38 expression occurs in the hematopoietic system during proliferative processes. Moreover, they suggest that CD38 expression is triggered at least in part by a certain cytokine(s) secreted by cancer cells. Finally, the results emphasize the prospective use of CD38 expression as a marker of tumor development and progression.