Entomopathogens, diseases of insects, are suggested as a possible new generation of safe, selective insecticides. Over a thousand pathogens have been isolated from insects. Many of these, associated with major insect pests, are potential candidates for development into microbial insecticides. Phases in the development of a microbial insecticide are discussed as well as factors (production, safety, efficacy, registration, non-technical) which may influence this development.