Peanut (Arachis hypogaea L.) seed proteins were resolved into arachin and non-arachin fractions, and composite two-dimensional polypeptide maps were prepared. Seed proteins were extracted with a buffer containing 2 M NaCl, 10 mM Tris-HCl (pH 8.2), 0.2 mM phenylmethyl sulfonyl fluoride and 0.002% NaN₃ and resolved into ten peaks by gel filtration on a Sephacryl S-300 column. Gel filtration of total protein extract yielded three molecular weight variants (490,000., 400,000, and 365,000) of arachin. Gel electrophoresis showed quantitative and qualitative differences in the protein and polypeptide composition of the three arachin variants. Nonarachin proteins obtained by this method were heterogeneous and distinct from the arachin. Two-dimensional gel electrophoresis revealed several differences in the polypeptide composition between arachin fraction IV and fractions II and III. Composite two-dimensional polypeptide maps of arachin and non-arachin revealed the presence of several polypeptides with similar isoelectric points and molecular weights between them. Arachin contained six molecular weight (between 15,500 and 68,000) classes of polypeptides with isoelectric points between 4.7 and 8.4 while nonarachin contained nine molecular weight (between 16,000 and 170,000) classes of polypeptides having isoelectric points between 4.7 and 7.9.