Seventy-two-hour LD50 studies involving the fenvalerate formulation, Pydrin 2.4 E.C., and the permethrin formulation, Ambush, were performed with male Swiss mice to compare the toxicity of the commercial formulations to that of the technical-grade pyrethroids. Comparison of the formulation ip and po LD50 values and the lethality of technical-grade pyrethroids revealed an increased toxicity of the technical-grade material when administered as the commercially formulated products. The calculated ip and po LD50 values for Pydrin 2.4 E.C. and Ambush were calculated to be 62 and 72 mg/kg, respectively, whereas those for Ambush were 429 and 424 mg/kg. Administration of doses of technical-grade fenvalerate which corresponded to the amount of fenvalerate contained in the calculated LD99 value of Pydrin resulted in no deaths. Administration of the LD99 value of Ambush, as the technical-grade product, resulted in no deaths following ip administration, whereas the po value resulted in 100% death. The data indicate an effect of the Pydrin formulation vehicle on fenvalerate toxicity, whereas the Ambush vehicle did not enhance permethrin toxicity. Technical-grade material in general was more toxic following po than ip administration suggesting the corn oil vehicle may have reduced ip absorption.