A selection of various conventional histochemical techniques, lectins and antibodies were used to identify the gonadotropic and somatotropic cells in the killifish, Fundulus heteroclitus pituitary. Distribution and variation of the gonadotropic cells and some histochemical reactions (PAS and Alcian Blue) largely parallel the cyclic changes in the gonads (GSI). Pituitary cells located in the ventral proximal pars distalis (PPD) and pars intermedia (PI) of the pituitary of the killifish, contain basophilic granules, which were positive to Alcian Blue and PAS reactions. These cells showed reactivity to different lectins, indicating the presence of Man (mannose) and/or Glc (glucose); GlcNAc (N-acetylglucosamine) and NANA (sialic acids); Gal (galactose) as well as GalNAc (N-acetylgalactosamine) sugar residues of glycoconjugates. These pituitary basophilic cells were stained with anti carp a,b GTH, and specially with anti carp b GTH; the maximal and minimal immunostaining, against the first antisera used, were observed during maturation/spawning period and during postspawning/resting phase, respectively. On the other hand, acidophilic cells located in the dorsal proximal pars distalis (PPD) of the pituitary gland of the killifish, were selectively stained with eosin, light green and/or orange G, when Haematoxylin-eosin, Haematoxylin-V.O.F and/or Alcian Blue-PAS-Orange G techniques were performed, respectively. These acidophilic cells were negative to PAS, Alcian Blue and lectins reactions; they contain proteins rich in different aminoacids and showed specific immunostaining against anti recombinant seabream growth hormone (anti rsbGH).