Sodium azide (SA) (NaN3) is well known as a potent mutagen in bacteria. In eukaryotes is a metabolic poison that traps oxygen excited, interfering with the activity of various enzymes. In Drosophila melanogaster, causes mitotic recombination in somatic cells, in response to chromosomal breakage. In addition, it has been observed that the treatment itself causes an apparent delay in the development of the larvae exposed. In this study, we evaluated whether the exposure to sublethal concentrations of NaN3 affects the development cycle (10 days at 25 °C) and tropisms such as the negative geotaxis of adult flies recovered. Wild-type, third instar larvae, were fed semichronically with serial dilutions of SA, from 0.125 mM to 1.8E-13mM. Each day, adult flies recovered were counted and separated, until all flies had emerged. Two groups were formed according to the time of hatching: 10-12 days and 13 or more days. The effect on treatment in the behavior of flies from two periods of hatching (10-12 and 13 or more days) was compared. Groups of 20 flies were put into a vial (15 ml of volume) connected through a channel of 6 mm with other vial (same volume). The frequency of flies that cross in one minute to the second vial was determined. 20 families per concentration were used. Sodium Azide treatment changes the frequency with which the flies went through the second tube. Although the response was not linear, a higher frequently of crossing to the second tube was found in flies that hatched among 10-12 days and were treated with 1.8E-12 1.5E-11 2.4E-7 of SA; In contrast, flies in group 13 or more showed a higher frequency of crossing only if was previously fed with 1.5E-11. When comparing the frequency of passage between groups (10-12 and 13 or more), differences in all concentrations were confirmed, except in the highest proven, 1.25E-1. Both of them, the treatment with SA, and the emergency period, determine the behavior of crossing on Drosophila melanogaster. These results show that exposure to genotoxins should be evaluated on several types of responses, which may be relevant to determine the real effect induced on organisms surviving to toxic exposures. Acknowledgements: To Banco de Moscas (Drosophila Stock Center Mexico) by provide the biological material, Faculty of Sciences, UNAM.