A comparative study of the carbohydrates and protein of five maize cultivars at 30 days after pollination (DAP) showed a higher protein content for the Supersweet variety, and better protein quality for the Maya Opaque-2, Nutrimaiz, the Supersweet, and the Hybrid L90 x L41, when compared to the Maya Normal. The lipid content also proved to be higher in the four genetically-modified cultivars in relation to the Maya Normal. In contrast, the Maya Normal and the Opaque-2 were higher in starch content, lower in total and reducing soluble sugars, and exhibited only very small amounts (approximately equal to 1%) of phytoglycogen, a water-soluble polysaccharide. Nutrimaiz and the Hybrid L90 x L41 had approximately half the starch of the Maya Normal cultivar, but presented an appreciable content of phytoglycogen (23-26%), which is typical for sugary maize mutants, and a higher amount of soluble sugars, mainly sucrose, in relation to Maya Normal. The Supersweet had about half the starch content and a very high (approximately equal to 24%) amount of soluble sugars, mainly sucrose, in relation to the Maya Normal cultivar. The Supersweet also had a negligible amount of phytoglycogen. Nutrimaiz and the Hybrid L90 x L41 showed a much higher proportion of grain in the ears and, as a consequence, a higher yield of dry solids at 30 DAP, when compared with the Maya Normal cultivar.