Earliness is a highly heritable trait and selection is an efficient method to decrease days to flowering in maize (Zea mays L.). In many tropical environments, earliness is important for a brief rainy season or for a specific cropping sequence. The evaluation of 15 cycles of selection at 13 environments has been performed in the present study to measure the direct effect of selection for earliness and the correlated response in other agronomic traits in the Compuesto Seleccion Precoz population.;Direct response to selection resulted in a decrease in time to flowering of 0.5 days per cycle of selection and most of the gain was obtained in the first three cycles of selection. The contribution of homozygotes was more important than of the heterozygotes for the mean of the base population although both were highly significant. Similar tendency was observed for the mean of the selected populations. The genetic drift was highly significant with assortative mating being the probable cause. The additive genetic variance accounted for 89% of the total genetic variation, based on the performance of cycles per se.;Correlated response as a result of selection for earliness caused a decrease in grain yield, plant height, ear height, grain moisture, and leaf area. For the mean of the base population, genes with additive effects determined the major contribution for grain yield, plant height, ear height, root lodging, stalk lodging, grain moisture, and leaf area. For the selected populations the homozygous contribution was important for plant height, ear height, grain moisture, and leaf area. The effect of random drift was important only for grain moisture.
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