The role of alpha-interferon (IFN) in initial treatment of multiple myeloma is controversial. We have conducted a trial of cyclophosphamide with and without low dose IFN in newly diagnosed myeloma. Thirty four patients, mean age 63 were all given cyclophosphamide 600mg/m2 IV every 21 days while 17 were randomised to also receive IFN at a dose equivalent to 6mU per week. In the IFN group 8/15 assessable patients (53%) had a greater than 50% reduction in paraprotein compared with 4/16 (25%) of controls (p < 0.05). However the median duration of response was the same in the two groups (IFN 8 months, controls 8.5 months). After a median follow up of 28 months there is no significant difference in survival. Toxicity including myelosuppression was commoner in the IFN group. These findings suggest that the addition of IFN to cyclophosphamide is not likely to offer major benefits in treating myeloma.