In the past several years many advances have been made in the field of protein metabolism. Under the stimulus of war especial interest has been directed toward protein metabolism after trauma of various sorts and during convalescence. The studies which will be summarized briefly here have, in the main, been carried out under the auspices of the Committee on Medical Research of the Office of Scientific Research and Development; many of them have been reported in an informal and preliminary manner at the Conferences on Metabolic Aspects of Convalescence, sponsored by the Josiah Macy Jr. Foundation.1At the outset it may be stated that the present state of knowledge leaves many problems yet unsolved, especially in regard to the mechanisms of the physiologic processes during periods of great wastage of nitrogen, when the organism consumes large portions of its vital tissue constituents in an effort to repair itself or