Pituitary gonadotropins (GTHs), follicle stimulating hormone (FSH) and luteinizing hormone (LH), are key regulators of vertebrate reproduction. However, in teleosts with testis of semi-cystic type and asynchronous spermatogenesis, as the flatfish Senegalese sole (Solea senegalensis), the physiological roles of FSH and LH are still not well understood. To gain insight into this mechanism, full-length complementary DNAs (cDNAs) encoding Senegalese sole FSHb and LHb subunits, and the common glycoprotein a subunit (CGa), were cloned and sequenced. The three cDNAs consisted of 550, 582 and 744 nucleotides encoding peptides of 120, 148 and 132 amino acids, respectively. Comparison of the deduced amino acid sequences of sole FSHb, LHb and CGa with those from other teleosts indicated that cysteine residues and potential N-linked glycosylation sites were fully conserved with respect to other percomorphs and salmonids. However, the primary structure of FSHb and LHb in pleuronectiforms appeared to be highly divergent. In situ hybridization of mature male pituitaries showed that fshb, lhb and cga mRNAs were localized in the proximal pars distalis and in the periphery of pars intermedia. Realtime quantitative reverse transcription-polymerase chain reaction indicated that the levels of all three transcripts in the pituitary of males increased during winter and spring, at the time when plasma levels of androgens raised and testicular germ cell development and spermatozoa production were stimulated. These results suggest that FSH and LH may regulate spermatogenesis in Senegalese sole similarly to that described for other teleosts with testis of cystic type and synchronous germ cell development. ; 12 pages, 5 figures, 1 table ; We thank J.V. Planas for critical reading of the manuscript. This work was supported by the PLEUROGENE project funded by a Genome Spain–Genome Canada joint program. M.J.A. was recipient of a fellowship from the Instituto Nacional de Investigacio´n y Tecnología Agraria y Alimentaria (INIA, Spain).