A new mutant, "black scale" (bs), in the adults of the malaria vector mosquito Anopheles stephensi is described. The genetic analysis of the mutant suggested that the phenotype is determined by a single, recessive, autosomal gene. Linkage analysis between bs and "diamond palpus" dp showed that the two genes are linked at a distance of 21.03 + 0.56 map units. The gene bs appears to exhibit complete penetrance and expressivity is constant.