Leptin, a hormone secreted by adipocytes, plays an important role in the regulation of metabolism and reproduction. The effect of leptin is mediated mainly via the long isoform of the leptin receptor (OB-Rb). Expression of leptin and its receptor has been identified in the central nervous system (hypothalamus, pituitary) and reproductive tract (uterus, ovary and placenta) in prepubertal gilts. Therefore, in the present study, the porcine OB-Rb expression was examined by a semiquantitative reverse transcription polymerase chain reaction (RT-PCR), in situ hybridization and Western blotting in the corpus luteum (CL) and ovarian stroma (OS) during the luteal phase of the estrous cycle (days 10-12 and 14-16) and two stages of early pregnancy (days 14-16 and 30-32). The OB-Rb gene expression in both ovarian structures was higher during early pregnancy in comparison to the mid- and late-luteal phase of the estrous cycle. Significant differences in OB-Rb gene expression between the two periods of the pregnancy were observed only in OS. The results of in situ hybridization are generally supported by data of semiquantitative RT-PCR. The CL expression of leptin receptor protein was significantly lower during early pregnancy compared to the cycle. In OS, the OB-Rb protein content was higher during pregnancy compared to the late-luteal phase of the estrous cycle. In summary, the obtained results indicate that leptin may participate in the control of pig reproduction at the ovarian level and have a direct effect on the ovary during both, the luteal phase of the cycle and early pregnancy. Moreover, changes in OB-Rb gene and protein expression in ovarian structures strongly suggest that their sensitivity to leptin varies throughout the luteal phase of the cycle and early pregnancy.