Quantitative changes in the chemical composition of stored corn infested with the grain insects Prostephanus truncatus, Sitophilus zeamais or Sitotroga cerealella were studied in the laboratory under the following conditions for each species: after infestation of samples by larvae, at the emergence of the first generation and after more than one generation. Changes occurred in the composition of all samples, the effect being more marked with larvae. Although no consistent pattern was evident, the nitrogen concentration of infested samples generally increased and the ether extract decreased. The total amounts of each constituent decreased in all samples, with up to 19% loss of energy content. Some of these changes may be attributed to selective feeding by each species, on specific regions of the maize kernel; this phenomenon was more apparent in the case of samples infested with larvae.