Styrene and styrene oxide were injected into the air space of fertilized chicken eggs at different times during an incubation period of 14 days. The toxicity of styrene and styrene oxide when injected on the fourth day of incubation revealed an LD50 of 40 mumol/egg and 1.5 mumol/egg, respectively. Malformations were found in 0-20% of the embryos, but never in the controls. The results obtained point to a need for further experimental, and possibly epidemiologic, studies on the consequences of styrene exposure.