Immunoexpression of androgen receptor (AR) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) was investigated in three generations of corpora lutea (CLs), found in the ovaries of rats on Days 1, 2, 5, 9, 14 and 20 of pregnancy. The youngest generation of CLs functioned during the whole pregnancy, whereas the older and the oldest generations underwent earlier regression. The newly formed CLs exhibited weak cytoplasmic 3beta-HSD expression. During subsequent days, a gradual increase in 3beta-HSD immunolabelling was observed, followed by a decrease on Day 20. In the older and the oldest CLs, surviving luteal cells demonstrated strong, although in the oldest CLs mostly perinuclear, 3beta-HSD immunoreaction. The newly formed CLs showed weak nuclear AR immunolabelling, which became stronger during the following days. On Day 20, luteal cells demonstrated a weaker nuclear immunoreaction. The older and oldest generations of CLs exhibited weaker and almost negative AR immunolabelling, respectively. Of special interest was the richly vascularised apical region of young CLs. Here luteal cells with more intensive 3beta-HSD staining predominated, whereas cytoplasmic AR immunoreaction was accompanied by positive or negative nuclear AR immunoexpression. The present studies showed differences in AR and 3beta-HSD distribution within various generations of CLs and within particular regions of the same young CL.