Developing seeds from four peanut (Arachis hypogaea L.) cultivars were obtained and classified into Immature, Low-Intermediate, Intermediate, High-Intermediate and Mature groups. Seed proteins were extracted from the defatted meals using either 2 M NaCl, 0.01 M Tris HC1 (pH 8.2) or 9.3 M urea, 5 mM K₂CO₃, 2% Nonidet P-40 and 0.5% dithiothreitol and examined by one and two-dimensional polyacrylamide gel electrophoresis. Two dimensional gel electrophoresis showed major qualitative and quantitative changes in seed protein composition during maturation. Several major protein components gradually disappeared while others increased in their content. Major changes in the polypeptide composition were observed between the Intermediate and High-Intermediate maturity stages. In addition, the arachin (major storage globulin of peanut) components were present from the very early stages of seed development. Variation in the amount of protein components indicate selective synthesis and modification of certain seed proteins during seed development.