Oil-continuous microemulsions provide an effective medium as a liquid membrane for extraction of proteins due to high solubilization and low miscibility in aqueous feed. Unlike the use of reverse micelles, this new method employs a preformulated cosurfactant-free nonionic microemulsion of high water content. The use of nonionic microemulsions for hemoglobin extraction demonstrates the potential for effective separation of proteins, amino acids, and other biochemicals. The extraction can be controlled by adjusting pH and microemulsion composition. It is enhanced by the addition of an appropriate liquid ion exchanger. The extraction results cannot be explained only in terms of ionic interactions.