Acute poisonings may require identification of the toxic agents. It is impossible for routine laboratories to provide a full spectrum of toxicological analyses, and clinicians should know the reliability of the clinical diagnoses of toxic agents. We performed a 1-year study of hospitalized acute poisonings to determine the agreement between the clinical assessment on admission and serum laboratory tests for eight common toxic agents. Blood samples were drawn in 665 (70%) of the 947 admissions. The total number of laboratory found agents (967) exceeded the clinically suspected (871) by 11%. The agreement between the clinical assessment and laboratory analyses was good for ethanol and paracetamol (kappa = 0.70 for both), whereas only moderate or fair for other agents (kappa 0.22-0.51). Sensitivities of the clinical assessments compared to the laboratory results were better for common than rare agents, and better for higher than lower serum concentrations. The four most common agents (ethanol, benzodiazepines, paracetamol, and opiates) had overall sensitivity of 82% for higher-than-median serum concentrations, whereas the other agents had sensitivities ranging from 14% to 71% for higher-than-median concentrations. The reliability of the clinical diagnoses varied to such an extent that agents, which are important to recognize for specific treatment, should be tested for.