p6e complementation between corn and fish, and rice and fish was evaluated for the purpose of establishing the required levels of each constituent in the mixture to obtain the optimum value in the biological evaluations for each diet. The optimum fish levels were around 10 and 6% for the corn and rice diets, respectively. Complementary levels of fish in the bean: corn and bean:rice diets were evaluated in the same manner. The best values in the biological evaluation were obtained with only 2% of fish. The economical analysis of these mixtures revealed that the nutritional value of the Central American rural diets can be increased with the introduction of fish in small quantities in the habitual diets, without increasing the family food expenses.