Aclacinomycin (ACM) is an oncostatic substance on the family of the Anthracyclines, with a proven activity in human and rodents. Splenic cells from C57BL/6 ACM injected mice by intraperitoneal or intravenous route four days before their sacrifice showed a significant increase in the proliferative and cytotoxic response respectively measured by incorporation of 3H-TdR and by the liberation of 51Cr when stimulated in vitro with irradiated mouse DBA/2 splenic cells. This response is doses dependent, and one can clearly observe different effects on the proliferative and cytotoxic responses at high doses. The cultures supernatants of splenic cells from mice treated with ACM during allogeneic stimulation showed a greater activity to induce the proliferation of a line of T cytotoxic cells dependent on Interleukin-2. Finally, the cytotoxic activity of splenic cells induced by the allogeneic stimulation in vitro, of mice treated with ACM, was found in a subpopulation of cells non adherent to plastic, mainly made up of lymphocytes.