The electrophoretic patterns of 13 loci were used to compare the three main T. cruzi zymodemes (Z) circulating in North/Northeastern Brazil (Br 1 through 3) with the four principal zymodemes present in Southeastern (BrA through D) Brazil. 2. Nei's standard genetic distances (D) obtained by paired comparison of the Brazilian zymodemes indicate the presence of four divergent groups, separated by D = 1.18. Zymodemes BrB and BrD presented heterozygous patterns for six and three loci, respectively, for alleles coding for isoenzymes of the BrA/Br 2 and BrC zymodemes. 3. The 7 principal Brazilian zymodemes were in turn compared with the 11 other zymodemes thus far identified in South America (Colombia, Bolivia, Paraguay and Chile). Numerical taxonomy demonstrated the presence of three main infraspecific categories ('groups') separated by D greater than 1.08. Each of these 'groups' could be divided into 2 or 3 subgroups at D greater than or equal to 0.50. 4. The wide range of zymodemes within a group separated by a genetic distance ranging from 0 to 0.95, the presence of zymodemes with variable numbers of heterozygous patterns (1 to 6), the detection of two homozygous zymodemes circulating sympatrically with their corresponding heterozygous zymodemes, and the circumstantial evidence that the majority of zymodemes carrying heterozygous profiles are found in the domestic sector of subtropical regions and always associated with Triatoma infestans, indicates that genetic recombination can also occur presently under certain conditions.
