Little information is available concerning lamins in the nucleus of germinal cells. In this paper we briefly describe and compare the organization of A- and B-type lamins in several mammalian spermatozoa. Nuclear lamin B is localized primarily in the postacrosomal sheath of human, bull and rabbit spermatozoa; lamin A/C is a major component of the equatorial segment in most of mammalian sperm, with the exception of rodents. In mouse sperm, devoid of equatorial segment, only lamin B appears to be expressed. The same happens in human pathological spermatozoa in which the equatorial segment is altered or absent.