Active specific immunotherapy of human solid tumors by use of enzyme altered cells appears to be a feasible approach. Our initial results, we believe, warrant continued effort in this area. There seem to be no adverse clinical effects to such treatment. In vitro assay methods, to document enhanced immunity, must be included in any immunotherapy program. Equally importantly, such test methods should be expanded for the earliest detection of adverse effects, such as blocking during the course of immunotherapy. The role of immunotherapy must be that of adjuvant treatment, and its only applicability will be in that role.