We address the impacts of regulations designed to reduce pesticide poisoning of farmers and farm laborers. Attention is concentratedon pre-harvest interval regulations that impose a time interval between pesticide application and harvest. The incidence of poisoning is determined by aggregate pesticide use, worker exposure, and toxicity. A dynamic, stochastic model of insect population growth is developed and used to measure the incentives for pesticide use. Increasing the pre-harvest interval has an ambiguous effect on the number of harvest worker poisonings. Pesticide taxation unambiguously reduces the number of worker poisonings. Theoretical results are quantified in a case study of mevinphos application on leaf lettuce in California's Salinas Valley. Copyright 2000, Oxford University Press.