In heterozygote state, we interogressed three chromosomal segments of Drosophila koepferae in D. buzzatii. The effect of each introgression was evaluated in the fertility of the segmental males, quantifying the amount of offspring produced. Through specific crosses method, we generated Drosophila segmental isolines carrying specific chromosomal introgression segments. The introgressions were monitored cytogenetically by the method of molecular markers of chromosomal asynapsis. The statistical analysis showed that none of the three segments evaluated, introgressed individually or in pairs, as well as cis or trans, do not produce sterility in the segmental males, as determined by the normal productions of offspring. Additional introgressions using other larger segments show that when the introgressions reach a minimum size of 31.15%, they produce sterility. It is concluded that the hybrid sterility genes present in the three segments evaluated did not act in strong epistasis, but show a pattern of gradual additive behaviour by requiring a minimum threshold size to produce sterility. Finally, we also isolated the smallest introgressing segment that has been reported for these species (2.19%), and for the first time we have managed to place it in homozygous state (data not shown), so we are now in the process of evaluating the ability to these segments in homozygous state.