The discrimination of poisoning from other conditions is essential. When multiple patients with similar clinical findings are seen, deliberate poisoning should be considered along with the possibility of resulting from accidental food poisoning, infection, diseases resulting from extreme circumstances, and mass hysteria. The diagnosis of causal poisoning chemicals based on clinical findings is essential. Breath odors, findings of vomitus, skin color, body temperature, autonomic nervous system findings, and seizures are important physical findings. On the other hand, laboratory findings such as ECG abnormalities, metabolic acidosis, increased serum hepatic enzyme levels, and increased serum blood urea nitrogen and creatinine levels are also useful in obtaining the correct diagnosis. X-ray films are useful in demonstrating several types of radiopaque drugs in the stomach. Rapid tests are valuable in diagnosing poisoning caused by such chemicals as paraquat and cyanides. Therapeutic diagnoses obtained by administering competitive blockers of specific receptors are also valuable when benzodiazepine or opiate poisoning is suspected. The final diagnosis of the causal chemical should be based on both the clinical findings and analytical results.