A multicenter phase II study of INTRON, recombinant alpha-2 interferon (Schering Corp, Kenilworth, NJ), in patients with relapsing or refractory myeloma was initiated. Patients received either intravenous therapy for two weeks followed by subcutaneous therapy or subcutaneous dosing from initiation of treatment. Of 38 evaluable patients, 19 were refractory and 19 had relapsed at entry. Twenty-five of 38 had received prior treatment with multiple drugs. Responses were seen among 2/19 refractory patients and 5/19 relapsing patients. Three of seven responders continue to respond for more than one year while receiving maintenance therapy. Most patients experienced improvement in bone pain, and one patient, with a complete response, had healing of bone lesions. Survival curves show a statistically significant improvement in survival for responders v nonresponders. INTRON was well-tolerated with only four patients discontinuing treatment due to adverse effects. Thirty-two percent of patients had hematologic toxicity requiring dose adjustment; however, there was no evidence of cumulative hematologic toxicity. No patients developed serum neutralizing factors to interferon. Additional trials are warranted to study the activity of INTRON in previously untreated patients.