The synthesis of specific keratins in differentiating amphibian epidermis has been studied by autoradiography after tritiated histidine injection, immunocytochemistry and immunoblotting. Most labeling is present in upper spinosus and corneous layers suggesting higher protein synthesis in these differentiating keratinocytes In the epidermis of the toad Bifo viridis and of the newt Triturus vulgaris most of the synthesized epidermal proteins arc keratins of acidic-neutral type, including K6, K16, and K17-like keratins of 45-60kDa Proteins of lower molecular weight and with basic pi are present in very low amounts or are absent. Ultrastructure immunolabeling for K6 and K16 keratins shows that they are associated with dense material among keratin filaments and with dense mucous granules. but not with monofilament bundles of differentiating keratinocytes After the release of mucous granules in upper keratinocytes of the intermediate layer and in pre-corneous keratinocytes. the immunolabeling for the above keratins is localized along the plasma membrane of maturing keratinocytes. This distribution is similar to that of actin, and suggests that actin together with K6, K16, and K17-like keratins may be involved in the process of extrusion of mucous-containing glycoproteins from differentiating, amphibian keratinocytes