BACKGROUND Elevated CO2 usually reduces levels of proteins and essential micronutrients in crops. The adoption of early maturing varieties may minimize the deleterious effect of climate change on farming activities. Legumes stand out for their high nutritional quality, so the objective was to study whether the atmospheric CO2 concentration affected the growth, yield, and food quality of early maturing cultivars of peas, snap beans, and faba beans. Plants grew in greenhouses either at ambient (ACO(2), 392 mu mol mol(-1)) or under elevated (ECO2, 700 mu mol mol(-1)) CO2 levels. Minerals, proteins, sugars, and phenolic compounds were measured in grains of peas and faba beans, and in pods of snap beans. RESULTS The effect of ECO2 depended on legume species, being more evident for food quality than for vegetative growth and yield. The ECO2 increased Fe and P in faba bean grains, and Ca in snap bean pods. Under ECO2, grains of pea and faba bean increased levels of proteins and phenolics, respectively, and the sugars-to-protein ratio decreased in pods of snap beans. CONCLUSION Early maturing varieties of legumes appear to be an interesting tool to cope with the negative effects that a long exposure to rising CO2 can exert on food quality.