Laboratory experiments carried out on marigolds and orange leaves suggested that volatilization was the most important process responsible for the short residual life of foliar applied chlorpyrifos. In order to control its volatility, the insecticide was incorporated into a series of materials, including abietic acid, abietic acid esters, phenolic resin, bitumen, montan wax and Pinechem (a sodium hydroxide digested pine wood material). Release rates were found to be highest for Pinechem and bitumen and lowest for phenolic resin and abietic acid esters. Emulsions (formed by adding the matrices to water, detergents and organic solvents) containing chlorpyrifos were tested on marigold plants and similar results were obtained. The toxicity of the formulations to the gelechiid Phthorimaea operculella and 3 of its parasitoids (Apanteles subandinus, Orgilus lepidus and Copidosoma koehleri) was tested in dishes to which the emulsions had been applied. The best controlled-release formulation was an emulsion based on abietic acid esters. For this formulation, the lowest dose required to achieve 100% mortality of the test insects was less than one-hundredth of that of the conventional formulation, for exposure of the insects for 24 h. none