Cell-to-cell communication by gap junctions was investigated in the female rat anterior pituitary gland from 10 through 45 days of postnatal development and in 60-day-old animals. Gap junctions initially appeared between adjacent folliculo-stellate cells on day 25. Their appearance in female rats was 5 days later than that observed in males (Soji et al., 1990). Gap junction number increased until the animals became 40 days of age, when they reached a level that resembled that found in adults. In addition, a correlation was evident between the frequency of gap junctions and stages of the estrous cycle, where they were most numerous during either proestrus or estrus. These results along with those previously published suggest that gap junction formation within the female rat hypophysis is in part modulated by both gonadal steroid hormones as well as prolactin.