Summary: GAO discussed the Environmental Protection Agency's (EPA) and the Food and Drug Administration's (FDA) regulation of pesticide residues in food. FDA is responsible for testing domestic and imported foods for pesticide residues to ensure compliance with EPA residue tolerances. The United States consumes an estimated 290 billion pounds of food each year, of which it imports about 43 billion pounds. GAO found that FDA: (1) cannot detect many pesticides; (2) lacks adequate information on pesticides used on imported crops; (3) does not test all imported foods on a regular basis; (4) generally does not test for pesticides that it cannot detect by the multiresidue method; (5) is unable to prevent the marketing of most adulterated foods because they move very quickly through the marketplace due to their perishability; and (6) is not authorized to issue civil penalties against growers and producers of adulterated foods. GAO also found that EPA: (1) lacks the data for determining safe residue limits and the health hazards of inert pesticides in groundwater; (2) plans to reassess tolerances for 390 older pesticides, but cannot ensure that established residue limits adequately protect health; and (3) has not set tolerance levels for inert pesticide ingredients. GAO believes that the uncertain health risks associated with chemical residues in food underlie the importance of effective food monitoring programs.