Eighty-four patients with myeloma were randomized to receive maintenance Intron A (Schering-Plough, Suffolk, UK), 3 mega units/m2 s.c. three times weekly or no treatment following induction therapy with cyclophosphomide, vincristine, doxorubicin, methyl prednisolone (C-VAMP), consolidated with high-dose melphalan (HDM) 200 mg/m2 + autologous bone marrow transplantation (ABMT). The patients have been followed up for a median of 52 months. Overall, median progression-free survival (PFS) from HDM was 27 months in the control group and 46 months in the Intron A group (< 0.025). For the 65 patients who achieved complete remission (CR) with HDM, there was a significant prolongation of remission (p = 0.02) for those who received Intron A and 49% of these patients remained in remission four years after high-dose treatment. However, for partial responders (PR) and nonresponders to HDM there was no significant prolongation of PFS. Overall, survival was also significantly better for the Intron A group, with 5 deaths versus 14 deaths in the control group (p = 0.006). Subsequently, 54 consecutive patients received the same HDM followed by rescue with peripheral blood stem cells after induction chemotherapy which included C-VAMP. Intron A was started in 45 of these patients at a median of 62 days which was comparable to the ABMT arm. The overall response rate in these patients was 79.62% (43/54-CR+PR) and the probability of survival at 18 months was 74.2% by the Kaplan Meier method.(ABSTRACT TRUNCATED AT 250 WORDS)