The amounts of [1-5]-bradykinin in ovary extracts were determined using gonadotropin-treated immature female mice. The bradykinin levels in the ovary were high at 2, 6, and 48 hr after injection of human chorionic gonadotropin (hCG) into pregnant mare's serum gonadotropin (PMSG)-treated mice. Northern blot analysis of total RNAs isolated from the PMSG/hCG-treated mouse ovaries indicated that the B₂ receptor mRNA was constitutively expressed. Bradykinin B₂ receptor protein was detected by Western blot analysis of the ovary extracts. In situ hybridization analysis revealed that the B₂ receptor mRNA is expressed in the granulosa cells of all growing follicles of ovaries from both gonadotropin-treated immature and mature female mice. The effect of bradykinin on the expression of the B₂ receptor gene was examined by RT-PCR analysis with the ovary previously cultured in the presence of bradykinin. Bradykinin treatment of immature female, gonadotropin-treated immature female, and mature female mouse ovaries brought about no apparent changes in the B₂ receptor mRNA level. The present data indicate that the level of B₂ receptor expression in the ovary is fairly constant, and that the biological effect elicited by bradykinin in this organ may be dependent upon concentrations of the ligand produced by operation of the kinin-kallikrein system.