The chemistry, metabolism, toxicology, mutagenicity, and carcinogenicity of maleic hydrazide have been reviewed. There is little doubt that this chemical is a mutagen and a carcinogen in cell cultures and animals, but no evidence is available on human carcinogenicity regardless of population exposure in manufacturing, agriculture, and the food chain (i.e., potato chips). An epidemiology survey should be conducted to ascertain possible human carcinogenicity in these populations. A long‐term ingestion experiment should be conducted in several animal species to establish whether maleic hydrazide is carcinogenic by this route. Biotransformation studies should be undertaken along with pharmacokinetic studies to obtain a better understanding of the chemical's metabolism and excretion. Such investigations would firmly establish whether the tolerance for maleic hydrazide should remain or whether the use of the compound should be banned under the Delaney Amendment.