The effects of ovine luteinizing hormone (oLH) and a synthetic analog of luteinizing hormone releasing hormone, des-Gly10 [D-Ala6]-LHRH ethylamide acetate salt (LHRH-A), on gonadal development and on in vitro steroidogenesis in the female phase of the protogynous sex-reversing Monopterus albus were investigated at different periods of the seasonal cycle. At the postspawning stage, oLH induced a precocious sex reversal with marked proliferation of interstitial Leydig cells and development of spermatogonial cysts in the gonads, and enhanced in vitro production of unsaturated androgens. However, such oLH effects were insignificant in females during the early prespawning stage: some spermatogonial cysts appeared, but no proliferation of Leydig cells took place. During both the postspawning and early prespawning stages, LHRH-A stimulated growth of the oocytes with increased yolk content. Gonadal steroid metabolism by females at early prespawning stage was not affected by LHRH-A within the brief experimental period. In the postspawning period, LHRH-A caused a change in the in vitro steroidogenic profile from a postspawning pattern to that of a typical prespawning female pattern with increased production of estrogens and two unknown metabolites, and decreased production of 5 alpha-androstan-3 beta-OH-17-one.