Various hormones were analyzed during the course of a reproductive cycle in the cichlid fish Oreochromis niloticus: plasma levels of the gonadal steroids l7g-estradiol (E2), testosterone (T), 17,209-OH progesterone (17,20flP), gonadotropin (taGtH), and plasma and pituitary concentrations of prolactin (tiPRL-j and tiPRLII) and growth hormone (tiGH). Two categories of fish were sampled and sacrificed on days 1 and 3 postspawning and at 3-day intervals thereafter: typical incubating females (INC), and nonincubating females (NI), deprived of their eggs just after spawning. Such deprivation is known to suppress maternal behavior and to accelerate ovarian development and especially vitellogenesis, thus shortening the mean interspawning interval. In both groups, variations of the plasma concentrations of E2 and T appeared to depend on ovarian stages, and differences between groups appeared to reflect underlying différences in the kinetics of ovarian development. The observation of noticeable levets of 17,20g-P in plasma before spawning, when high values of taGtH could also be detected in NI females, suggests the implication of this progestin in the control of final maturation events, as in some other teleosts. Moreover, 17,205-P, which was still detected a few days after spawning, but at low concentrations and only in the plasma of INC females, might play a role at the beginning of the reproductive cycle in incubating females (maternal behavior and/or slowing down of ovarian growth). The pituitary and plasma profiles of both tiPRLs isoforms appeared to depend mainly on the kinetîcs of ovarian development in each group of fish, suggesting a role during the beginning of vitellogencsis. However, the variance of plasma tiPRLjj, which was significantly enhanced during maternal behavior in INC females, also suggests an implication of this hormone in the control of that behavior. Concerning tiGH, comparison of the plasma profiles in INC and NI fish also suggest an influence on th