An adhesive organ is a prominent characteristic of the genus Idiosepius. Histological, histochemical and ultrastructural methods were applied to elucidate the nature of secretion of the epithelial cells of three Idiosepius species. The adhesive organs of Idiosepius biserialis and Idiosepius pygmaeus consist of five distinct cell types that can be distinguished morphologically and by the composition of their secretions. Histochemical analysis revealed that three cell types contain different sugar units and basic proteins, whereas the interstitial cells lacked secretory material. Acidic and sulfated substances were absent in Idiosepius secretions. The adhesive organ, but not the secretory material of the glandular cells, contained O-linked oligosaccharides. The histochemical analysis of the secretory products suggested that adhesion and release are not effected by a "duo-gland" adhesive system as in Euprymna scolopes. Idiosepius presumably uses a transitory adhesion, perhaps induced by secretion of a highly viscous gel. Release might be caused by contraction of the mantle musculature and/or chemical release mechanisms such as dilutors or enzymes.