Twenty-two patients with measurable metastatic renal carcinoma were treated with human .alpha. lymphoblastoid interferon (3 million U/m2 of body surface area) in 3 times a week for 6 wk; 21 were evaluable for response and toxicity. One patient had a partial regression of disease lasting 39 wk and another had a minor response. Six patients had partial or minor response in 1 area but no change in the disease elsewhere (mixed response); they were classified as having stable disease. An additional 7 patients had no change in measurable disease and in 6 the disease progressed. The tumor regressions by metastatic site were 4 of 14 patients, pulmonary; 3 of 4, soft tisue; 1 of 9, bone (? soft tissue); none of 3, mediastinal; none of 4, renal; none of 5, liver; and none of 10, other abdominal sites of tumor. The side effects were fever (101.degree.F-103.degree.F), chills, malaise, anorexia, minor (10%-20%) decrease in performance status, and weight loss. Interferon apparently had some activity against metastatic renal carcinoma, although clinically useful responses were quite infrequent. While lung metastases appeared to be more responsive than those at other sites, careful examination of the data suggests that this simply reflects differences in the bulk of the metastatic disease. Smaller metastases appear more likely to respond than bulky metastases.