AbstractDrosophila melanogasteris being investigated for its potential to aid in identifying priority chemicals for teratologic study. The method encompasses treating larvae over the entire metamorphosis period, i.e., from the egg through three instar stages to pupa formation, by incorporating the test chemical into the medium. Adult flies are systematically examined under a binocular microscope for external morphological anomalies. Data from treated flies can be compared with those from concurrent control flies using standard statistical tests. Results from this developmental work reveal a dramatic and reproducible response ofDrosophilato various chemical treatments. Validation studies, testing known teratogens and nonteratogens, are necesary before such a system can be incorporated into existing teratologic screening regimens.