Adoptive chemoimmunotherapy has cured experimentally induced tumors in animals, but its clinical use has been limited. Six patients were treated with refractory neoplasms in a Phase I study with cyclophosphamide (CPM) and alloactivated haploidentical lymphocytes. Patients received an immunosuppressive dose of CPM (800 mg/m2) followed by haploidentical lymphocytes primed in vitro with alloantigens in mixed lymphocyte culture (MLC). One week later patients received a second infusion of alloactivated lymphocytes expanded in T-cell growth factor (TCGF). The total number of cells given to each patient progressively increased, with a single patient receiving 35.5 X 10(9) cells. Transient febrile responses and delayed-type hypersensitivity reactions at the intravenous sites were the only toxicities noted. A complete clinical response lasting 12 weeks was seen in a single patient with diffuse histiocytic lymphoma. Our experience indicates that adoptive chemoimmunotherapy can be given to patients safely and merits further clinical testing.