The general toxicological information required by the Environmental Protection Agency (EPA) under the Federal Insecticide, Fungicide, and Rodenticide Act for pesticides sold in the United States was discussed. The amount of data needed to determine the toxicity of a particular pesticide varied according to the use pattern, inherent toxicity, date of first registration, type of registration, and completeness of adverse effects reporting by the manufacturer. For tests of acute, subchronic, and chronic toxicity; oncogenic, teratogenic, reproductive, mutagenic, and genotoxic effects; and metabolism, the use of rats, mice, rabbits, dogs, hens, and guinea- pigs was recommended. The animal of choice depended upon the particular toxicity test in question. Reentry protection and spray drift tests were also required for some pesticides. Testing was mandatory for the active ingredients of pesticides utilized in the manufacture of other pesticides and pesticides used as end products. End use formulations were also tested for oral, dermal, and inhalation toxicity and eye and skin irritation. The findings of the acute toxicity tests must be displayed on the pesticide label as the signal word Danger, Warning, or Caution. The testing of the inert ingredients in a pesticide formulation was conducted separately for each ingredient. The requirements and guidelines for testing pesticides were frequently revised and improved. The authors conclude that awareness of the toxicity testing conducted for registered pesticides may facilitate clinicians in their treatment selections. Clinicians are encouraged to report cases of pesticide exposure to the manufacturer and the EPA.