Summary Histomorphological staining demonstrated 2 types of cells in the pallial gland of the mantle of Lithodomus lithophaga: gland cells containing glycolipoprotein and interstitial cells, containing lipid droplets. Biochemical analysis aiming at separate and evaluate lipidic and peptidic components were carried out by lipid extraction, T. L. C. separation and colorimetric assays. Phospho- and sulfalipids were separated from non-polar lipids. Sialo-cerebrosides (gangliosides) are missing. Hydrophobic peptide component was extracted and aminoacid analysis was made. The presence of acid (phosphate) group in the gland secretion is discussed in relation to the function of the secretion (Ca uptake and rock boring). The prominent glycogen storage is considered as an important energy source to be used for osmotic work and to synthesize glycosidic stones for glycolipo-protein secretion.