To determine the site of oxytocin in human ovaries and its relationship with ovarian steroids, oxytocin and steroid hormones were measured in ovarian tissues, ovarian vein, and peripheral blood. Corpus luteum had significantly higher oxytocin, estrone, estradiol, and progesterone concentrations than corpus albicans and ovarian stroma (p = less than 0.01 to less than 0.001). Oxytocin concentrations in corpus luteum correlated significantly with estrone, estradiol, and progesterone. Oxytocin in corpus luteum increased from 14.0 +/- 1.8 ng/gm of wet weight in early to 30.8 +/- 0.9 ng/gm in midluteal phases (p = less than 0.001). Reverse phase high pressure liquid chromatography showed similarity between oxytocin in corpus luteum and synthetic oxytocin. Ovarian vein draining corpus luteum had significantly higher plasma oxytocin (11.8 +/- 1.5 pg/ml) than those without corpus luteum (2.1 +/- 0.2 pg/ml) or in the peripheral blood (2.9 +/- 0.3 pg/ml) (p = less than 0.001). Oxytocin in corpus luteum correlated significantly with its ipsilateral ovarian vein level of oxytocin, estrone, progesterone, and 17 alpha-hydroxyprogesterone. Our findings demonstrate that oxytocin is present and probably produced in corpus luteum and secreted into its ovarian vein; it may regulate corpus luteum release of progesterone, 17 alpha-hydroxyprogesterone, and estrone.