The effect of different doses of aclarubicin, an anthracycline antitumor antibiotic and different regimens of its use on the cellular and humoral immune response in mice with semisyngeneic carcinoma 755 was studied with using multifactor experiments. The resulting quantitative data were computer processed and 2nd order polynomial equations reflecting regressive relationships between the indices being studied and expressed graphically were developed. The analysis indicated that it was possible to use multifactor experiments for studying relationships between various factors defining this or that effect and in particular for determining optimal interaction between therapeutic and immunological activity of antitumor drugs.