Individual Drosophila melanogaster, with or without heads, can be trained to lift their legs to avoid electric shock. This behavior is similar to the operant conditioning previously demonstrated in intact and headless cockroaches. More than 90% of headless wild-type flies learned to our criterion. In contrast, three mutants (dunce, cabbage, and turnip), originally selected for failure to learn in an olfactory discrimination paradigm, tended to perform poorly in this new learning situation. The difference in learning behavior between normal and mutant flies is distinguishable in individuals and may be useful for mosaic analysis.