Identification of human milk proteins and formulation of a two-dimensional map is a first step in a project which intends to survey human milk proteins by two-dimensional electrophoresis. Thirty-four proteins have been identified using the Iso-Dalt method of separation and Western blot with immunoprobes. Identification confirms that milk is species-specific, and, therefore, breast feeding confers a decided advantage for the infant. Using antisera for identification has revealed relationships between molecules which have not been previously noted. The antibody recognizes a common epitope between the IgA alpha chain and lactoferrin, and between the IgD d chain and beta casein. Milk protein concentrations vary longitudinally, diurnally, and individually. Identification of the proteins contributes meaning to the varying patterns. Knowledge of human milk proteins will help to elucidate human nutrition and health needs.