Ten patients with active definite or classical rheumatoid arthritis (RA) were treated with oral minocycline (maximal daily dose 400 mg) during 16 weeks in an open study. Seven patients reported side effects (in most cases vestibular) leading to premature discontinuation in one. Half of the efficacy variables improved significantly after 4 weeks of therapy. At the end of the study all variables were significantly changed compared with their pretreatment values. We conclude that minocycline may be beneficial in RA. This effect needs to be confirmed in controlled studies.