Abstract. Prolactin is an anterior pituitary hormone involved in many endocrine activities and plays and essential role in reproduction. Its receptor (PRLR) was detected in various tissues including brain, ovary, placenta, an uterus in several mammalian species (BOLE-FEYSOT et al. 1998). Reproductive performance of sows is a crutial point in pig production with significant economic importance and may be estimated with the help of markers. Porcine prolactin receptor gene is said to be a candidate genetic marker for reproductive traits. It has been mapped to porcine chromosome 16 (Vincent et al. 1997). There is a C/G SNP in PRLR gene (KMIEC et al. 2001) at the position of 203 (GAN: U96306) which eliminates an AluI cleavage site. The effect of this polymorphism on litter size in various breeds has been estimated (VINCENT et al. 1998, ROTHSCHILD et al. 1998, VAN RENS et al. 2002, KMIEC and TERMAN, 2004, DRÖGEMÜLLER et al. 2001, KORWIN-KOSSAKOWSKA et al. 2003). The influence of the bovine hormone variant was also estimated (RATNA-KUMARI et al. 2008). The aim of the study was to estimate PRLR AluI polymorphism effects on litter size in Hungarian Large White (HLW) and Hungarian Landrace (HL) breeds.