To meet the needs of an ever-growing world population for food and fiber, agriculture uses an arsenal of chemicals to control insects, weeds and other pests that compete with man in the agricultural arena. In addition to their intended effect, many of these biologically active materials affect non-target organisms including man himself. There is concern about the resulting occupational exposure of those who work in agriculture and the environmental health of those who live in rural areas. Unintended side effects from the use of agricultural chemicals are further complicated by the dispersal of these substances well beyond the area of immediate use, through food chains, atmospheric transport, irrigation runoff, percolation to and diffusion through ground water, sometimes giving rise to public health and environmental problems at a distance from the place of application. In addition to toxic substances introduced into the agro ecosystem by man, one must be concerned about naturally occurring agents including mfcotoxins, plant poisons, infective biological agents and the levels of certain heavy metals. The formation of toxic substances, many of them mutagenic, during cooking and other processing of food is a related problem. While acute effects are more immediate and somewhat readily discerned, chronic and genetic effects tend to be more obscure and sometimes surface in a crisis situation long after substantial damage has been sustained. Genotoxicity assays and epidemiological studies play increasing roles in predicting and evaluating long term effects of low-level exposure to toxic materials.