Histochemical methods used to investigate the appearance and the changes of the epithelial mucins produced by the lining and glandular epithelium of the chick embryo gizzard from the 7th day of incubation to hatching. Carboxylated, sulfated and neutral mucins appeared simultaneously at the superficial layer of the lining epithelium (7th day), at cells located in the inner part of the lining epithelium surrounding intercellular spaces (9th day) and at the tubular glands (15th day). During the period of incubation considered, an increase and decrease in the production of the various mucins were observed at the lining epithelium. However, a gradual increase of mucous production was detected at the ephitelial cells surrounding intercellular spaces (from the 9th to the 17th day) and at the tubular glands (from the 15th to the 21st day). Moreover, three different overlapping steps of mucous release were observed during the development of the gizzard. The histochemical characteristics and the trend of production of the mucous material in the gizzard during the embryonic development were different when compared with those found in the proventriculus (Sgambati et al., 1995). These differences are probably related to the different function of the mucins in the two parts of the stomach.