The toxic hazards associated with exposure to ethyleneimine (151564) (EI) are discussed. Uses in textile treatment, adhesives and binders, rocket and jet fuels, chemosterilant chemicals, and chemotherapeutic agents are listed among the applications of EI. The hepatotoxic and neurotoxic effects of EI in rats and rabbits are noted, along with its mutagenicity in Drosophila, Neurospora, and plants and induction of chromosome aberrations in human and mouse cell cultures. Research findings are summarized for carcinogenicity tests of EI and related compounds in rats, including induction of injection site sarcomata, pancreatic tumors, mammary fibroadenoma, injection site fibroma, and renal carcinoma. The comparative carcinogenicity of EI and related compounds is discussed. Tumor induction is also described in mice injected subcutaneously with aziridine (151564), a closely related derivative of EI. Also described is a study by the National Cancer Institute in which EI was used as a positive control compound. The author notes that the carcinogenicity of EI to humans depends upon the extrapolation of test results in mice and rats. Previous researchers have stated that, regardless of the EI derivative, the EI prosthetic moiety may be primarily responsible for the carcinogenicity of the molecule.