The expression of CD14+ macrophages, CD4+, CD8+ lymphocytes and mRNA of inducible nitric oxide synthase (iNOS) was investigated in the endometrium of repeat breeders with subclinical endometritis [experimental group (EXP), n = 10] and healthy [control group (CTRL), n = 10] cows. The cows were selected on the basis of repeat breeding (3 unsuccessful inseminations), clinical and cytological examinations (> 10% polymorphonuclear neutrophils in uterine smears obtained by cytobrush). From all the cows endometrial biopsies were collected and the presence of CD14+, CD4+ and CD8+ cells in the endometrium was evaluated immunohistochemically using semi quantitative counting method. The mRNA expression of iNOS was determined using reverse transcription-PCR. In general, there were no significant differences between EXP and CTRL groups in the expression of CD4+ and CD8 + lymphocytes in all endometrial structures. In contrast, we observed a higher number of CD14+ macrophages in repeat breeding group compared to the control cows, however, this difference was slightly pronounced. CD14+ cells were detectable only in the stratum compactum and stratum spongiosum. The statistically significant (p < or = 0.05) higher expression of iNOS mRNA was measured in the cows with subclinical endometritis compared to the healthy animals. Our results suggest that the increased expression of CD14+ macrophages and iNOS mRNA may be associated with embryonal mortality in repeat breeding cows with subclinical endometritis.