Accumulation pattern and compositional changes in peanut (Arachis hypogaea L. cv. Florunner) arachin were determined by monitoring arachin from seeds of different maturities by gel filtration, two dimensional gel electrophoresis and amino acid analysis. The results indicated that arachin deposition was maximum between Immature and Intermediate stages, and that the arachin monomer increased more than the polymer during seed maturation. Arachin polypeptides with apparent molecular weights of 70,000: 32,000 and 29,000 increased in abundance with increasing maturity while a 50,000 molecular weight polypeptide decreased during seed maturation. In addition, amino acid composition of arachin differed in seeds of different maturities. These data suggest that arachin polypeptides are not deposited in equal amounts but individual polypeptides accumulate in different proportions during peanut seed maturation.