The efficiency of selection for resistance to aflatoxin development caused byAspergillus flavusL. ex Fries, in maize(Zea maysL.) grain was studied in three CIMMYT lowland tropical maize populations. Seed samples of each population were inoculated with a spore suspension of cultures ofAspergillusspp. known to produce aflatoxins. Inoculated seeds were maintained at 85% RH in plastic boxes kept at room temperature. At 50% germination, seed samples were planted in the field. At flowering time, selected plants were bulk pollinated. After three cycles of selection, gains for tolerance to aflatoxin formation and improvement for agronomic characters were evaluated. The results indicate there are differences in aflatoxin accumulation between different genotypes and cycles of selection. Populations 22 (DMR) and 28 (DMR) were the most damaged and Population 31 DMR suffered the lowest infection. The study suggests that there are differences in aflatoxin production between the maize genotypes tested. However, our results failed to show that tolerance to aflatoxin development can be accumulated through a recurrent selection breeding scheme.