We studied the effects of adoptive immunotherapy with lymphokine-activated killer (LAK) cells plus interleukin-2 or therapy with high-dose interleukin-2 alone in 157 patients with metastatic cancer for whom standard therapy had proved ineffective or no standard effective treatment was available. One hundred eight patients were treated with 127 courses of LAK cells plus interleukin-2, and 49 patients were treated with 53 courses of high-dose interleukin-2 alone. Of 106 evaluable patients receiving LAK cells plus interleukin-2, 8 had complete responses, 15 had partial responses, and 10 had minor responses. The median duration of response was 10 months among those with complete responses and 6 months among those with partial responses; the patient with the longest complete response was still in remission 22 months after treatment. Of 46 evaluable patients treated with high-dose interleukin-2 alone, 1 had a complete response (remission greater than 4 months), 5 had partial responses (2, greater than 3, greater than 5, 7, and greater than 11 months), and 1 had a minor response. Seven of the total of nine complete responses still remain in remission. Hypotension, weight gain, oliguria, and elevation of bilirubin and creatinine levels were common, but these side effects resolved promptly after interleukin-2 administration was stopped. There have been four treatment-related deaths among these 157 patients. This immunotherapeutic approach can result in marked tumor regression in some patients for whom no other effective therapy is available at present. Determining its ultimate role in cancer therapy awaits further attempts to increase the therapeutic efficacy of treatment and decrease its toxicity and complexity.