The formation of serum albumin in chicken liver has been shown to proceed via an intermediate stage in which newly formed albumin is bound to microsomes. This bound albumin is apparently formed within 2-3 minutes, but its release requires 15-20 minutes and is readily blocked by metabolic inhibitors. Comparison of the effectiveness of various agents in releasing this newly formed albumin suggests that the albumin is bound on or in the lipide-rich membrane of the microsome. After release by desoxycholate the material is indistinguishable from native serum albumin in its physical and chemical properties. The mechanisms of the synthesis of proteins in liver are discussed, and insofar as possible related to the results with serum albumin.