Very late activation ( VLA, β1; α1; α5, α9) integrins were studied by immunoblotting and immunohistochemistry in the testes of sexually mature rats. All integrin subunits were present in membrane fractions of homogenized testes. Immunohistochemistry revealed that the anti β1 antibody recognized peritubular cells and the basement membrane of blood vessels. Immunoreactivity was also demonstrated in the lamina propria, basement membrane, and the basal cytoplasm of Sertoli cells. In elongating spermatids, β1 integrin was localized to the acrosome. The α1 subunit was expressed in peritubular cells and in the lamina propria. In the adluminal compartment, round spermatids were stained diffusely for the α1 subunit. Immunoreactivity for α1 integrin was found additionally in the acrosomes of elongating spermatids shortly before their release into the seminiferous tubule lumen. The α5 subunit was expressed in the acrosomes of elongating spermatids as well as in their distal cytoplasm during stages III–VI; the cytoplasmic lobes of elongate spermatids and/or residual bodies also appeared to be immunostained in seminiferous tubules at stages VII–VIII. The α9 subunit was immunolocalized only in the basement membrane and in peritubular cells. These data suggest that integrins are involved in spermatogenesis, in particular in the process of spermatid maturation.