The Drosophila melanogaster fruitless gene encodes multiple male-specific transcription Factors that are hypothesized to regulate a hierarchy of genes responsible for the development of male courtship behavior. Here we show that there are dramatically increased levels of the protein product of the male courtship behavior gene yellow associated with male-specific Fruitless protein in a subset of neuroblasts in third-instar larval male brains. We hypothesize that yellow is downstream of fruitless in a male courtship behavior developmental genetic pathway. (C) 2002 Elsevier Science (USA). A-H rights reserved.