The effect of interferon on the health-related quality of life in multiple myeloma was assessed in two trials carried out by the Nordic Myeloma Study Group (NMSG). In both trials, the EORTC QLQ-C30 questionnaire, supplemented with 11 items relating to interferon toxicity, was used. The first was a randomized controlled trial (NMSG 4/90) evaluating the addition of interferon alpha -2b to melphalan and prednisone during induction, maintenance and relapse. During the first 12 months, patients on interferon reported more chills, fever, fatigue, pain, nausea/vomiting, appetite loss and dry skin than the control patients, and a slight reduction of global health and quality of life. From 12 months onward there were no significant differences in any score between the two groups. In a later trial (NMSG 5/94) evaluating the effect of high-dose chemotherapy with stem cell support in patients under 60 years of age with newly diagnosed myeloma, interferon was used as maintenance. During the maintenance phase, symptom and toxicity scores were not significantly different from those in control patients under 60 years of age in the previous trial. Thus, interferon appeared to be well tolerated after high-dose chemotherapy with stem cell support.