The gland cells located in the upper lip of the cladoceran Daphnia were studied by histochemical reactions to establish the chemical nature of some substances they synthesize. Neutral polysaccharides were found to be present, but acid glycosaminoglycans absent. Large amounts of proteins and ribonucleoproteins are also present, lipid substances were not detected. Immunohistochemical methods failed to reveal alpha-amylase in the labral gland cells, though the enzyme was detected in the cells of the intestine. The secretion products of the labral gland cells are probably glycoproteins. The results are discussed in terms of the possible roles of these substances in the animal's physiology.