The majority of all patients with poison exposures in the United States are children. The evaluation and management of poisoned patients may be aided by the use of laboratory assays, ranging from basic assessments not uniquely indicated for the poisoned patient to highly sophisticated laboratory tests with very specific indications. Literature concerning poisoning in pregnant patients is evaluated and recommendations regarding the utility of pregnancy testing in poisoned females are discussed. Recent studies evaluating the use of toxicology testing in pediatrics have concluded that the use of comprehensive toxicology screening in pediatric patients is costly and does not affect the medical management of most poisoned patients. The utility of focused quantitative serum assays to determine serum levels of particular poisons is reviewed. Toxicology tests used for detection of drugs of abuse, with a particular focus on the capabilities and limitations of such tests, are discussed. The potential pitfalls that occur when toxicology tests are obtained indiscriminately, are misapplied, or are misunderstood are analyzed. Hair sampling as nonemergent toxicology testing for drugs of abuse is discussed.