The objective of this study was to evaluate the safety and possible efficacy of IFN-beta-1a for the treatment of patients with rheumatoid arthritis (RA). Twenty-two patients with active RA were enrolled in a phase II randomized, double-blind, placebo-controlled trial of 30 microg IFN-beta-1a by weekly self-injection for 24 weeks. The primary outcome of the study was safety. Secondary outcomes included the proportion of patients achieving an American College of Rheumatology (ACR) 20 response at 24 weeks. There were no significant differences in adverse events reported in the two groups. Fewer than 20% of patients in each arm of the study achieved an ACR 20 response at 24 weeks (P = 0.71). Sixty-nine percent of patients receiving IFN-beta and 67% receiving placebo terminated the study early, most of them secondary to a perceived lack of efficacy. Overall, IFN-beta-1a had a safety profile similar to that of placebo. There were no significant differences in the proportion of patients achieving an ACR 20 response between the two groups.