The pharmacokinetics of antineoplastic drugs based on compartmental models are combined with deterministic exponential growth models of tumors containing drug-resistant and sensitive cells. Model predictions for single-drug therapy are compared with in vivo data obtained by other investigators for L1210 t-cell leukemia in mice treated with BCNU and Ara-C and for in vitro treatment of L1210 with Ara-C. The model and data compare favorably in terms of rate of tumor growth and duration of drug action for both constant infusion and bolus delivery of the drugs.