In 53 F1 sows (Zlotnicka Spotted boars × Polish Large White sows) the insulin-like growth factor 1 (IGF1) and estrogen receptor (ESR) genes were assessed as candidate genes for total number of piglets born (TNB), number of piglets born alive (NBA), litter weight at birth (LWB), litter weight at weaning (LWW), number of piglets weaned (NPW), average piglet weight at weaning (AWW) and gestation length (GL). The IGF1 locus genotype (microsatellite sequence) was found to affect (P≤0.01) the TNB, NBA and GL when based on analysis of sows with all litters born. No association between reproductive traits and ESR genotype was found in any restrictive site. However,interesting appeared the results of the analysis including an interaction between ESR genotypem in three polymorphic sites where almost all traits investigated appeared associated (P≤0.05) with ESR genotype. However, due to the limited number of animals, conclusions on the relationship between gene polymor-phisms and reproduction traits must be considered as preliminary, and thus treated with care.