THE molecular weight of egg albumin quoted in all but the most recent literature is 35,000–36,000, a value based on the early osmotic pressure measurements of Sorensen1, the ultracentrifuge measurements of Svedberg and Nicols2, Nicols3, and Sjogren and Svedberg4, as well as the diffusion data of McBain5. More recently, however, there has been general agreement that this value is too low; the sedimentation constant and diffusion data quoted by Svedberg and Pedersen6, for example, as well as the osmotic pressure data summarized in Table 1, indicating a value of 43,000–46,000.