Serum prolactin has been measured in single blood samples collected within the first 22 post-partum months from 97 nursing mothers from an urban area (Bukavu) of Zaïre. Nursing mothers are hyperprolactinemic, higher serum prolactin levels being associated with more frequent suckling episodes per day. Furthermore, serum prolactin declines rapidly in mothers who are giving the breast less than four times per day: the levels are within the normal range found in non-lactating women after the 6th post-partum month. Among mothers giving (...) the breast more than six times per day, serum prolactin does not decline significantly during the 1st post-partum year. (shrink)