Arginine vasopressin (AVP) was determined in plasma and follicular fluid in 28 women in an in vitro fertilization program. In 23 women, follicular fluid was collected by laparoscopy during general anesthesia, and in 5 women, it was collected transvaginally with no such anesthesia. Plasma AVP increased markedly from its basal (preanesthesia) value in the first group, whereas it did not change in the second group. AVP concentrations were approximately 10-fold lower in the follicular fluid than in the plasma collected simultaneously in the anesthetized women. AVP levels were not significantly different in plasma and follicular fluid in the women of the second group. AVP concentrations were similar in ovarian venous and brachial venous plasma in 4 women during surgery. These results indicate that AVP concentrations in follicular fluid are equal to or lower than those in plasma and that AVP concentrations are not higher in efferent blood from the ovary than in peripheral blood.