The purpose of the present study was to evaluate the nutritive quality of the Ayocote bean (Phaseolus coccineous) and to determine whether it could be increased by the addition of methionine. Methionine (0.6%) and salt (4%) were added at the beginning of cooking, 30 min before the beans were cooked or at the end when they were cooked, dried and ground. The beans were dried with or without broth. Proximate analysis, amino acids determination, available lysine, in vitro and in vivo digestibility as well as PER were determined in the bean flours. A second experiment was carried out using diets supplemented with increasing amounts of methionine (0.1-1%). The addition of this amino acid improved the chemical score, but methionine continued to be the first limiting amino acid. The beans dried with broth showed lower chemical score values than those dried without broth. The concentration of available lysine was lower in the beans dried with broth; the content of it in the beans was, however, still high. No significant differences were found in the PER's of the beans supplemented with different concentration of methionine. The addition of the amino acid can be effected at any step of cooking, since it was found that the thermic treatment did not reduce the utilization of the methionine added.