This study investigated the genotoxicity of Lapachol (LAP) evaluated by wing spot test of Drosophila melanogaster in the descendants from standard (ST) and high bioactivation (HB) crosses. This assay detects the loss of heterozygosity of marker genes expressed phenotypically on the fly's wings. Drosophila has extensive genetic homology to mammals, which makes it a suitable model organism for genotoxic investigations. Three-day-old larvae from ST crosses (females flr³/TM3, Bd s x males mwh/mwh), with basal levels of the cytochrome P450 and larvae of high metabolic bioactivity capacity (HB cross) (females ORR; flr³/TM3, Bd s x males mwh/mwh), were used. The results showed that LAP is a promutagen, exhibiting genotoxic activity in larvae from the HB cross. In other words, an increase in the frequency of spots is exclusive of individuals with a high level of the cytochrome P450. The results also indicate that recombinogenicity is the main genotoxic event induced by LAP.