Six zygotically expressed genomic lociof Drosophila melanogaster, N, bib, mam, neu, DlandE (spl), have previously been found to be involved in the commitment of ectodermal cells as neuroblasts. We have studied phenotypes induced by various mutant alleles at these 6 loci in imaginal epidermal cells, in order to assess possible implications of the genes in functions other than early neurogenesis. When homozygous, any of these mutations exceptbibaffected the development of bristles and compound eye in various ways. These range from cell death to the production of additional bristles and several defects in ommatidial patterning, depending on the allele used. In contrast clones ofbibhomozygous cells exhibited wild-type phenotypes. The differences found in the expression of the neurogenic genes are discussed with respect to a hypothesis on the genetic control of neurogenesis.