A method of antitumor therapy is described in which administration of a chemotherapeutic drug, encapsulated in liposomes, is supplemented by administration of an immunostimulating cytokine. The cytokine is preferably also encapsulated in liposomes. In tumor models for lung and colon carcinomas, this method produced a significantly greater therapeutic effect, as evidenced by survival rate and tumor size, than a combination of the effects produced by the free or liposome-encapsulated components administered individually.