The larval salivary glands of Drosophila melanogaster, which are widely used for cytogenic studies, are also useful for studying the regulation of specific protein synthesis during differentiation. These glands synthesize and secrete massive amounts of a glue which attaches the pupae to the substrate during metamorphosis. We find six major proteins in this glue. They show wide quantitative and qualitative variation among wild-type strains of D. melanogaster. Four of the proteins are glycosylated, and one of these is further modified so that its mobility on SDS polyacrylamide gels is greater than the mobility of its unmodified precursor. The glue proteins begin to be made at about 106 hr after egg deposition. The synthesis of four of the proteins begins coordinately, while one protein begins to be made slightly earlier and one slightly later. The proteins are synthesized for approximately 14 hr until puparium formation, when the glue is released from the salivary glands. Synthesis of five of the glue proteins stops abruptly within a few minutes after the glue is released. The sixth protein continues to be synthesized for at least 30 min after glue release.