As the number of multicellular mucous glands increases in the skin ofXenopus laevis larvae during metamorphosis, the acid mucopolysaccharide (AMPS) content of the skin increases also. Purification of this skin AMPS by polyacrylamide gel electrophoresis revealed a major band characteristic of adult mucous secretion. Incorporation of14C-galactose into this band increases during metamorphosis, but there is still a substantial synthesis of this material in premetamorphic skin that lacks mature mucous glands. This raises the question of whether the epidermal cells that had been making mucus in premetamorphic skin stop this activity as mucous glands develop, or whether they are discarded and replaced by a new population of epidermal cells that do not make mucus unless they develop into a mucous gland.