To examine the occurrence of signs and symptoms of Reiter's syndrome (RS) in female sexual partners of males with RS we have investigated 43 female consorts of 42 males, originating from 72 consecutive patients suffering from RS or suspicion of RS (SRS). Anamnestic mono-, oligo- or polyarthritis occurred in 14 of the 43 females (32,6%) as compared to 28 out of 311 randomly selected interviewed controls (9,0%). Five of the 43 females had RS and 7 had SRS, (27,9%). However, the diagnosis could have been possible with only anamnestic information in 6 (14%) as compared to 7 out of 311 controls (2,3%). Taking into consideration the 30 males whose sexual partners were not investigated, the theoretically counted values still differ significantly from those of the controls (p less than 0.01). A history of urogenital and, on the other hand, nasopharyngeal or pulmonary infections involvements preceded equally frequently the first or further joint attacks. Evidence of chlamydial infection was found in 53,5% (32/43) of the partners while Yersinia antibodies measured by ELISA occurred with the same frequency as among healthy blood donors. We would like to stress the importance of various infectious involvements, especially sexually transmitted diseases, as etiological agents in joint attacks in females who are sexual partners of males with RS.