In testis, the expression of tumor suppressor protein p53 is stronger than in other tissues suggesting a role for it in spermatogenesis. We have studied the expression of p53 in both unirradiated and gamma-irradiated rat testis using the stage-specific model of rat seminiferous epithelium. Our results show that p53 is expressed during meiosis in normal rat spermatogenesis and its expression is localized to the preleptotene-early pachytene spermatocytes. The most prominent expression is in zygotene - early pachytene spermatocytes (stages XIII-I of seminiferous epithelium). After irradiation p53 levels increased in a time and a dose-dependent manner being highest with the doses of 6.0 and 12.0 Gy and 4 h after irradiation. This increase occurs in the same cells that normally express elevated levels of p53. These results support the view that p53 is involved in meiosis of the male rat and we suggest that p53 has a role in recombinational processes and/or formation of the synaptonemal complex. We also demonstrate that p53 takes part in the response of primary spermatocytes to irradiation gamma-induced DNA damage.