The present study evaluated the localization of luteinizing hormone receptors (LHR) and galectin-3 (Gal-3), a beta-galactoside-binding animal lectin, in the mature mouse ovaries by immunohistochemical analysis. Intense LHR immunoreactivity was detected in the active corpus luteum (CL), whereas expression of Gal-3 was high in the regressing CL and atretic follicle. In the CL of pregnant mice, LHR immunoreactivity was intense, but Gal-3 expression was low. Thus, LHR and Gal-3 had opposite patterns of expression in mature mouse ovaries, suggesting that both proteins have stage-specific expression patterns and are possibly involved in CL formation and regression.