Extensive compilation of material safety information on Methyl Ethyl Ketone Perioxide (MEKP), the active ingredient in catalysts for polyester resins. The review discusses the more dangerous industrial product, the commercial hardeners are dilute and stablized. Carcinogenicity: Mice developed malignant tumors after being given a total dose of approximately 7 mg. There is an extensive review of animal toxicity testing. Can be neutralized with 20% NaOH solution. -- AATA