EGF was localized in human fetal, adult and cryptorchid testis and seminoma using an immunohistochemical method. Leydig cells of adult testes stained intensely for EGF while those of fetal testes showed weak staining reaction. In addition, some spermatogonia and occasional peritubular myoid cells of adult testis stained positively. In cryptorchid testis, there were clusters of Leydig cells interspersed between seminiferous tubules with varying staining intensities. The number of positively stained cells in the cryptorchid testis were fewer than that in adult testes. The decrease in the number of Leydig cells producing EGF may account for the spermatogenesis arrest and infertility associated with this disorder.Intense staining of the cytoplasm of seminoma cells was observed, suggesting that the high production of EGF may be related to their invasive property. In conclusion, EGF is produced by human testis and Leydig cells are the principal source of this cytokine. EGF was localized in human fetal, adult and cryptorchid testis and seminoma using an immunohistochemical method. Leydig cells of adult testes stained intensely for EGF while those of fetal testes showed weak staining reaction. In addition, some spermatogonia and occasional peritubular myoid cells of adult testis stained positively. There were clusters of Leydig cells interspersed between seminiferous tubules with varying staining intensities. The number of positively stained cells in the cryptorchid testis were fewer than that in adult testes. The decrease in the number of Leydig cells producing EGF may account for the spermatogenesis arrest and infertility associated with this disorder. irritable of the cytoplasm of seminoma cells was observed, suggesting that the high production of EGF may be related to their invasive property. In conclusion, EGF is produced by human testis and Leydig cells are the principal source of this cytokine.