BR-105 and BR-106 are important tropical maize populations, which were submitted to a high-intensity reciprocal recurrent selection, generating the IG-3 and IG-4 synthetics. Using 30-microsatellite loci, we measured and compared the genetic diversity of these populations and their synthetics. The populations did not differ significantly regarding the amount of genetic diversity. As a consequence of selection, genetic variability losses, in terms of mean number of alleles per locus, proportion of polymorphic loci, and gene diversity did occur and were greater in the synthetic IG-3 than IG-4. In the synthetics, the number of loci in adherence to Hardy-Weinberg proportions was superior to that observed in the populations. The Wright's mean fixation index was higher than the mean value expected for outcrossing species (5%) indicating a slight excess of homozygotic individuals in both populations. The genetic distances confirmed the favourable effects of one cycle of recurrent selection, as the synthetics became more isolated in comparison to the original populations.1343277286