Some histochemical aspects of carbohydrates, proteins and lipids were studied in the swimbladder of seabream, Sparus aurata and seabass, Dicentrarchus labrax. In both species, swimbladder development occurs in two stages: (1) inflation and (2) expansion, respectively. No important differences in histochemical distribution of glucidic, proteic and lipidic macromolecules were observed during the swimbladder development. Glycoproteins containing mannose and/or glucose sugar are present in the swimbladder (gas gland, wall and rete mirabile) of both species, but glycogen was observed only in the gas gland of Sparus aurata swimbladder. Proteins rich in different aminoacids, except those rich in tryptophan, as well as carboxyl but not sulphated glycoconjugates were observed in both species. Neutral lipids and phospholipids are also important compounds of the swimbladder. Abnormalities such as hyperinflation and non inflation are common for both species, but no important histochemical differences were detected in normal and abnormal seabream and seabass swimbladder.