We have investigated chemotaxis of polymorphonuclear granulocytes (PMN) from 7 well characterized RA patients with intense disease activity, before and after steroid treatment. Increased spontaneous and directed granulocyte migration was observed in 6 out of 7 patients before steroid treatment. In 5 patients these parameters were reduced after treatment. In contrast to this, decreased chemotaxis of polymorphonuclear granulocytes (PMN) from patients with Rheumatoid Arthritis (RA), have been reported earlier. This has been suggested as a partial explanation of the increased morbidity of these patients. Plasma levels of Complement C3d were initially increased in all patients and were slightly reduced following treatment. PMN migration in highly active RA cases is increased and responds markedly to steroid treatment, in contrast to the complement activation. The mainly unaffected, increased levels of plasma C3d might, in part, explain the early recurrence of symptoms often seen when steroid medication is withdrawn. Our results contrast with earlier findings and need to be confirmed in further studies.