An integrated water insoluble chemical delivery/metabolic activation/rat embryo culture system is described. In initial studies corn oil was used as the solvent and diallate as the substrate. Increasing concentrations of diallate dissolved in corn oil caused embryonic growth retardation in vitro. The presence of a metabolic activity system did not potentiate the effects of diallate in corn oil. The rat hepatic microsomal monoxygenase system was enzymatically active even in the presence of high concentration of corn oil in the rat serum incubation media. Thus, the failure of the metabolic activation system to potentiate the toxicity diallate in corn oil is not due to an enzymatic deficiency of the hepatic metabolic activation system.