Evidence is reviewed for a dose-dependent reversal of response in mosquito oviposition, in which a compound that attracts or stimulates oviposition may repel or deter oviposition at a higher concentration. On the basis of a review of structure-activity relationships in compounds affecting mosquito oviposition, 5 hexanoic acid derivatives were selected for field tests with Aedes aegypti ssp. formosus in Kenya. Egg counts were increased most by methyl hexanoic acid and 5-methyl-2-hexanone, and the presence or absence of a methyl branch affected egg numbers more than the difference between a carbonyl and a carboxylic acid functional group. Hexanoic acid increased egg counts at low release rates, but decreased them at higher release rates.