The main seed proteins of Pisum and faba beans are the storage proteins synthesised in the seed and subsequently utilised to supply nitrogen and carbon for biosynthesis during germination and seedling development. There are two major families of storage proteins, legumin and vicilin. Legumins are hexameric proteins comprising of 6M r 60 000 subunits which, as isolated from mature seeds, show considerable charge and size heterogeneity. Vicilins are a less well-defined group of proteins consisting largely ofM r 50 000 subunits and non-equimolar amounts of lower molecular weight subunits. A third storage protein, convicilin, is also present in peas and beans. It is a vicilin-type protein with vicilin immunological determinants. Proteins homologous to legumin have been found in Arachis, Glycine, Vigna unguiculata, Lupinus, Cicer, Lens and Lathyrus. Equivalent vicilin-type proteins occur inPhaseolus vulgaris, Glycine, Arachis andVigna unguiculata. The storage proteins have an unusual amino acid composition related to their biological role. They are multimeric and readily undergo association/dissociation reactions. They show a high degree of charge and size heterogeneity, partly caused by co and post-translational modifications and partly due to gene divergence.