Leptin, the product of the OB gene, is a 16-kDa polypeptide of 146 amino acid residues produced mainly by adipocytes that regulates metabolism and reproduction. The actions of leptin are mediated mainly via the long form of the leptin receptor (OB-Rb). The identification of leptin and OB-Rb mRNAs and proteins in human and mouse endometrium, and placental trophoblast suggests that leptin may be involved in the implantation process. Thus, the aim of this study was to compare the expression levels of porcine OB-Rb mRNA and protein in the endometrium and myometrium during mid- and late-luteal phases of the oestrous cycle (days 10-12 and 14-16, respectively) as well as during two stages of pregnancy respondent to the beginning of the implantation process (days 14-16) and the post-implantation period (days 30-32), and in trophoblast during both periods of pregnancy. OB-Rb gene expression in endometrium during the examined stages of pregnancy and the mid- and late-luteal phases of the cycle was at the same level. In contrast, in myometrium leptin receptor gene expression decreased on days 14-16 of pregnancy compared to both phases of the cycle, and on days 30-32 of pregnancy in relation to late-luteal phase. OB-Rb protein expression in the tissues was lower during the examined stages of pregnancy in comparison to the mid- and late-luteal phases of the cycle. In trophoblast, OB-Rb mRNA and protein expression was higher on days 30-32 than during days 14-16 of pregnancy. In conclusion, our results might suggest that leptin can participate in the control of pig reproduction by exercising its action at the uterine and trophoblast level and have a direct effect on these organ during both the luteal phase of the cycle and early pregnancy. Moreover, changes in OB-Rb gene and protein expression in tissues of pig reproductive tract strongly suggest that their sensitivity to leptin varies throughout luteal phase of the cycle and early pregnancy.