The use of a wide range of chemicals to destroy pests and weeds is an important aspect of agricultural practice in both developed and developing countries. Undoubtedly, this has increased crop yield and reduced postharvest losses. However, the expanded use of such pesticides expectedly results in residues in foods, which has led to widespread concern over the potential adverse effects of these chemicals on human health. It is clear that the possibility for exposure to pesticides is greatest among farm workers. Also, it is exceedingly plausible that less controlled and regulated uses of pesticides may offer the greatest opportunity for exposure to toxicologically significant quantities. Very limited epidemiological data are available for evaluation of the health effects of pesticides on humans. Only a small proportion of a population is likely to receive a pesticide dose high enough to cause acute severe effects; however, many more may be at risk of developing chronic effects (such as cancer, adverse reproductive outcome, and immunological effects) depending on the type of pesticide they are exposed to. The pesticides currently in use include a wide variety of chemicals with great differences in their mode of action, uptake by the body, metabolism, elimination from the body, and toxicity to humans. With pesticides that have a highly acute toxicity but are readily metabolized and eliminated, the main hazard lies in acute, short-term exposures. With others that have a lower acute toxicity but show a strong tendency to accumulate in the body, the main hazard is connected with long-term exposure, even to comparatively small doses. Other pesticides that are rapidly eliminated but induce persistent biological effects also present a hazard connected with long-term, low-dose exposures. Adverse effects may be caused not only by the active ingredients and the associated impurities, but also by solvents, carriers, emulsifiers, and other constituents of the formulated product. This review attempts to describe several aspects of the problem.