We report a summary of a Phase I clinical trial of the partially purified MAF-containing supernatant of RPMI-1788 human B-cell lymphoblastoid lymphokine conducted in 39 patients with advanced cancer. The trial was conducted in four parts: two subcutaneous and two intravenous routes and schedules of administration. Dose limiting toxicity in the subcutaneous trials was volume dependent. The intravenous trial was remarkably well tolerated so that the maximum tolerable dose exceeded expectations. The study demonstrated modification of the immune system including an increase in skin test reactivity, an increase in absolute lymphocyte counts, alteration in the monoclonal lymphocyte antibody markers, and an increase in MAF activity. Toxicity in the intravenous trial was limited to transient febrile reactions that were ameliorated by increasing the infusion time. Three objective tumor responses were observed.