Pesticide use is one of several factors that have permitted maintenance of our supply of food in spite of continuing increase of the population. However, the use of biologically active compounds poses potential problems of toxicity. If the compound is used at any stage of food production, residues or derivatives may persist in food and the entire population may be exposed to the trace amounts of the material. The human body burden associated with long-term exposure may or may not be associated with illness. Persistent environmental contaminants such as pesticide residues have long been suspected to be implicated in cancer etiology. Organochlorine chemicals are persistent, lipophilic compounds commonly present in the environment. Some of them demonstrated carcinogenic activity in laboratory animals. Controversy still exists concerning their carcinogenic potential in humans. To answer this question, clinical toxicology laboratories should propose validated methodologies able to identify and quantify pesticide residues in biological samples. An example of chromatographic method dedicated to organochlorine residues is presented here and illustrated by results obtained in a healthy population (104 men, 147 women). Only 17.9% of the samples were free from detectable amounts of pesticides and p,p'-DDE 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene was the most frequently detected residue (66.5%). Hexachlorobenzene was found at detectable level in 13.5% of the samples.