By sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis the plasma membranes from porcine lymphocytes contain at least 30--35 glycopolypeptides and one or more glycolipids to which one or more of 12 purified lectins bind. The specificities of binding generally followed the same pattern as those of the reaction of the lectin with intact pig lymphocytes. Some lectins (e.g., the isolectin pair, Agaricus bisporus lectins A and B and a group consisting of the Lens culinaris A and B isolectins and the closely related Pisum sativum lectins) bind to almost identical populations of plasma membrane components and compete with each other for all their binding sites. Others (e.g., Concanavalin A and the Lens culinaris-Pisum sativum group and a group consisting of phytohemagglutinin-L, Ricinus communis lectin-60 and Ricinus communis lectin-120 bind in a cross reactive manner to some common binding moieties but, in addition, to certain nonshared ones. Still others (e.g., soybean agglutinin, peanut agglutinin and wheat germ agglutinin) do not share any common binding moieties with the other lectins. The amount of lectin binding and the number of membrane components to which a lectin binds is directly related to the Ka of binding of the lectin to the intact lymphocyte. Those with high Ka (Cocanavalin A Lens culinaris lectins, Pisum sativum lectins, phytohemagglutinin-L), bind to 20-30 different components giving very complex binding patterns while those with lower Ka (Agaricus bisporus lectins, wheat germ agglutinin, peanut agglutinin, and soybean agglutinin) bind to 8--13 components with easily distinguishable patterns. Soybean agglutinin binds almost exclusively to a glycolipid fraction while for the others one or more glycopolypeptides served as the major lectin-binding molecule. The Ricinus lectins, two lymphocyte toxins, bind to essentially every plasma membrane component to which the mitogen phytohemagglutinin-L binds, in fact competing for most of those plasma membrane moieties which bind phytohemagglutinin-L.