Various aqueous ovicidal formulations, some of which pose minimum hazards for higher organisms, are described for use against Aedes aegypti (L.). These ovicides appear to attack mainly layers of the eggshell which resist water permeability, an attack which causes the egg to dehydrate and collapse under ambient conditions. Humidity effects were studied before and after treatment. Basic and acidic formulations containing both nonpolar and polar compounds were found effective against either dry or moist eggs exposed to ambient conditions after treatment. The basic mixture contained a nonpolar long-chain aliphatic amine such as octylamine emulsified in an aqueous solution of a polar compound such as ethanolamine or urea, and the acidic mixture contained a nonpolar fatty acid such as octanoic acid in aqueous polar mer-capto acid. Nonpolar compounds alone in water were ovicidal under special conditions. An emulsion of fatty acid in water was effective against eggs exposed to high humidity before or after treatment, and aqueous fatty amines were ovicidal for eggs exposed to high humidity after treatment. Fatty amines, ranging widely in chain length and polarity, were evaluated against both larvae and eggs, Relative larvicidal activities correlated roughly with ovicidal activities, The least larvicidal of these amines, 6-amino-l-hexanol, used at 0,6% in water with 0.1 % decyl alcohol and 6% urea, provided a good ovicide, Of all the ovicides tested, it is presumably the least hazardous to higher organisms.