Factors affecting attraction of the Mexican fruit fly,Anastrepha ludens(Loew), to the odor of a bacterium isolated from the fly, were evaluated in laboratory experiments. The odor was not attractive to newly emerged adults. For sugar-fed, yeast-hydrolysate-deprived flies, attraction to the bacterial odor began when flies were 1d old, peaked when flies were 5–7 d old, then declined steadily as flies aged further. Generally, bacterial odor was attractive to sugar-fed flies and unattractive to sugar-deprived flies. The odor was most attractive to sugar-fed, yeast-hydrolysate-deprived flies but was also highly attractive to flies fed both sugar and yeast hydrolysate. Flies were attracted to bacterial odor during all times of the photophase although attraction was less very early and very late in the photophase than at other times. Flies irradiated with gamma rays were about 20% less responsive to the odor than unirradiated flies.