Ovarian function was evaluated prospectively in 16 female rheumatoid arthritis patients in the childbearing age. None of the patients was using oral contraceptives. The control group included 31 women with tubal sterility. Serum levels of estrone, 17 beta-estradiol and progesterone were assayed and used to determine an estrogen index and a luteal index. An ovulatory score was calculated as the sum of the estrogen and luteal indices. Estrogen levels were lower in the rheumatoid arthritis group than in the control group, but the difference was not significant. No statistically significant difference was found for progesterone levels, suggesting that luteal function was normal in the rheumatoid arthritis patients. The rheumatoid arthritis group had a significantly lower mean ovulatory score reflecting a decreased likelihood of ovulation as compared with the control group (p < 0.01). This abnormality may explain why fertility is reduced in women with rheumatoid arthritis.