Drosophila pseudoobscura were used to study the effect of three atmospheric pollutants (dichloroethane, trichloroethylene, and tetrachloroethylene) on the induction of three enzyme systems: acetylcholinesterases (AchE), P450 monooxygenases (P450), and glutathione S‐transferases (GST), the latter two biotransformation enzymes involved in the detoxification of xenobiotics. The effect of the pollutants on the fruit flies was evaluated under laboratory conditions, in a hermetic container, in tests conducted for periods of 24 and 72 hours with various pollutant concentrations. The enzyme activities of the exposed fruit flies were then measured by spectrophotometric and spectrofluorometric methods. GST and P450 activity was induced in Drosophila exposed to these three pollutants, at levels related to the pollutant concentration and exposure time.