Injection of actinomycin D (AMD) and fluorouracil (FU) into late third instar larvae brought about a fairly constant spectrum of phenodeviations in the imago of various genotypes ofDrosophila hydei including wild type. Common phenes were eye facet disarray, fusion of tarsal segments and to a lesser extent also eye reduction. AMD-reduced eyes ofwhite-mottled mutants also showed darker pigmentation than untreated controls.Notch mutants were more sensitive to AMD than non-Notch animals, as regards leg and bristle phenocopies.The most obvious difference between the two substances was their differential effect on bristle formation. AMD caused supernumerary bristles of thesplit mutant type, whereas FU tended to suppress bristle formation. The spectrum of malformations, especially after AMD treatment, resembled the temperature-sensitive phenes of certainNotch alleles ofD. melanogaster and suggests that AMD interferes with the transcription of the complexNotch gene.