The role of the lymphatic system in the absorption and biodistribution of antitumor agents and monoclonal antibodies is under investigation. Antitumor agents are delivered at high concentration to lymphatics and regional lymph nodes when entrapped in liposomes. Similarly, monoclonal antibodies given subcutaneously are delivered with high efficiency to regional lymph nodes where they bind specifically to lymphoid cells. Extensive metabolic and pharmacokinetic studies of antibodies directed against both normal and malignant cell types have been carried out in rodents. The pharmacological principles that have emerged from studies in rodents have been applied to the design of clinical protocols for the detection of malignant melanoma and T-cell lymphoma. In addition to studies on lymphatic malignancies, the carrier systems developed for selective delivery of antitumor agents and monoclonal antibodies to the lymphatics are being applied to therapy of human immunodeficiency virus (HIV)-induced acquired immunodeficiency syndrome. Initial studies indicate that liposome-entrapped dideoxycytidine triphosphate (ddCTP), a compound which blocks viral replication by inhibition of viral reverse transcriptase, is more effective in killing T-cells infected with HIV than is free ddCTP.