[en] Antisera to mammalian pituitary and placental hormones have been used to identify and localize the different cell types in the pituitary of the barbel (Barbus barbus, L.). The immunocytochemical labeling employed the immunoperoxidase technique or the immunogold silver staining procedure. Corticotrophic and prolactin cells, visualized using antisera to human adrenocorticotropic hormone and ovine prolactin (PRL), respectively, occur in the rostral pars distalis (RPD). Antisera against mammalian gonadotropins [ovine folliclestimulating hormone (FSH); bovine luteinizing hormone] or porcine growth hormone selectively cross-react with two different cell populations occupying the major part of the proximal pars distalis (PPD). Thyrotropic cells, stained by an antiserum to whole human thyroidstimulating hormone preabsorbed with porcine FSH, are scattered throughout the PPD and found amongst growth hormone and gonadotrophic cells. The majority of pars intermedia cells are stained with anti-melanophore stimulating hormone whereas the scattered PAS positive cells are revealed by both anti-ovine PRL and anti-bovine placental lactogen (or chorionic somatomammotropin). The latter antiserum also cross-reacts with the PRL cells of the RPD. Our results indicate that the distribution of the different cell types in Barbus barbus is similar to that described in other families of teleosts. This report is also the first demonstration of antigenic similarity between mammalian placental lactogen and fish prolactin.