A reduction in the incidence and severity of rheumatoid arthritis is seen in pregnant women. Relaxin, a hormone of pregnancy, has been implicated in decreased immune responsiveness. Consequently, the effects of relaxin and estradiol valerate, alone or in combination, were assessed in the development of adjuvant-induced arthritis in the rat. Combination hormone therapy reduced adjuvant-induced paw inflammation. Radiographic analysis of the tarsal joints showed that estradiol valerate plus relaxin treatment minimized soft tissue damage and bone changes when compared to vehicle-treated arthritic controls. These results indicate that relaxin may be a factor in reducing inflammation during pregnancy.