Studies are reported which follow the changes in starch, sugar, fresh and extraction residue weights of peanut fruit parts during maturation. Observations are also reported on the lipid content of the seed. Starch and sugar contents reached maximum levels first in the pericarp (hull) and then the seed coat (testa). Starch maxima occurred at early and middle maturity (stages 3 [10 mg] and 7 [10 mg]) and sugar maxima at a stage approaching middle maturity and at middle maturity (stage 6 [47 mg] and 8[9 mg]), respectively. In the seed, starch reached a maximum just beyond middle maturity (stage 9 [55 mg]) and then remained constant. Sugar content increased throughout maturation and lipid content became maximum at full maturity (stage 13 [415 mg]) then declined to 385 mg at over-maturity (stage 15). The role of regulating substrate supply to the developing seed seemed to shift from the pericarp to the seed coat with increasing maturity. Observed increases in fruit residue weight suggest that the pericarp is competing with the seed for metabolic resources during the late maturity stages.