Data were collected on 176 consecutive cases of drug overdose evaluated in an emergency department. Quantitative serum toxic screening (TS) was performed for 164 (93%) of these patients; positive results were noted for 133 patients (81%). Six classes of drugs (ethanol, benzodiazepines, salicylates, acetaminophen, barbiturates, and tricyclic antidepressants) were responsible for nearly 70% of all drug detections and were associated with 80% of all admissions in this patient sample. Only two patients (1%) had drug-specific treatment initiated because of TS results. In 12 patients (7%), TS confirmed substances for which specific treatments had been initiated on clinical grounds. Four patients (2%) had drug-specific treatment discontinued because of TS results. Thirty-two patients (19%) were admitted to a medical service; however, only seven patients (4%) were admitted primarily because of TS results. All other patients were admitted because of clinical abnormalities that required inpatient care. It is concluded that only a few drugs are responsible for most drug overdoses. Moreover, TS results rarely change the treatment or disposition of overdose patients; these decisions are typically based on clinical parameters.