A molecular understanding of an insect gene can be facilitated by analysing the phenotypes of mutants for that gene. Protocols were developed for both chemical and gamma-ray mutagenesis in Aedes aegypti using the white (w) gene as an assay. Wild-type adult males were subjected to varying doses of either ethyl methanesulphonate (0. 1%, 0.5% or 1%) or gamma rays (1500 R or 3000 R), mated to females homozygous for the recessive w mutation, and progeny screened for the w phenotype, indicating non-complementation. The expression of newly induced w alleles was either complete or mosaic. Gamma-ray mutagenesis resulted in high (1.65 or 6.39%, depending on dose) induction of mutant alleles for the w gene, but not for a different gene, red-eye (0.15%). Gamma-ray-induced w alleles did not revert at a reasonable frequency following additional irradiation, suggesting that the high rate of gamma-ray-induced w mutagenesis is not due to a transposon insertion event.