We raised an antibody against a synthetic peptide corresponding to amino acids 155-174 of human retinoic acid receptor alpha (RAR-alpha). The sequence is highly homologous in all RARs and their isoforms. When mouse and human RARs (alpha, beta and gamma) expressed in Cos cell were analysed with immunoblot, all receptors gave a specific 51 K signal. Mouse RAR-gamma gave an additional signal corresponding to 58 K. In human teratocarcinoma cells (F9) both 51 and 58K molecule sizes were detected. The RAR expression in F9 cells was slightly down-regulated in charcoal-stripped culture medium and returned to normal level after retinoic acid treatment. The 51 K protein was found in all ovarian and uterine samples, but the quantity of the 58 K protein varied in different species and organs, being highest in the mouse uterus and the rat and human ovary. Using immunohistochemistry the RARs were found in the nuclear compartment. In the rat uterus, positive immunoreaction was found mainly in the nuclei of epithelial, uterine glandular and stromal cells. In the rat ovary, positive reaction was found in the nuclei of germinal epithelial, follicular and stromal cells.