The purpose of the present research was to determine the differences which could exist between immature and mature pigeon pea in gross chemical composition and protein quality, raw and cooked, as well as their respective supplementary value to rice, and to mature and immature corn and sorghum. The chemical composition data showed only small differences in proximate composition between the mature and immature grain. The cooking process did not affect chemical composition. Based on the FAO/WHO amino acid reference pattern, immature pigeon pea was more deficient in threonine than mature pigeon pea, which was limiting in valine. Both grains were limiting in sulfur amino acids. The protein quality of the immature grain was higher than that of the mature grain, and both responded positively to cooking, suggesting the presence of antiphysiological substances in both. Amino acid supplementation studies demonstrated that both the immature and mature grain responded to methionine addition, the first limiting amino acid, and to tryptophan, the second limiting amino acid. The effects were more marked when samples were cooked. Both types of grains were good supplements to rice, when added in amounts of 10-20%. Mature pigeon peas supplemented relatively well the proteins of sorghum, immature and mature corn, at the 20, 30 and 20% levels, respectively. The differences found could be explained on the basis of the amino acids limiting cereal grains and pigeon peas protein.