AbstractDrosophila melanogaster males were exposed to gaseous 1, 2‐dibromoethane at concentrations lower than those used in aerosol treatments of suspected mutagens by other investigators. Premeiotic stages appear to be more sensitive than postmeiotic stages to gaseous mutagens. At an exposure of 125 ppm.hr, significant numbers of mutations were induced in spermatids, spermatocytes, and spermatogonia. Since this exposure increased the mutation rate in spermatogonial stages by a factor of 20–40 over the spontaneous rate, it appears that the lowest detectable exposures may be much lower than 125 ppm.hr for 1, 2‐dibromoe