Clinical variables, and especially their relation to the ECG, have been studied in 153 cases of poisonings by tricyclic antidepressants (TCA). The mean age of the patients was 34 years. Amitriptyline poisoning accounted for 112 (73%) of the cases and the mean dose ingested was about 1 000 mg. Coma was present in 87 patients (57%) and on admission 40 (26%) had a systolic blood pressure (BP) below 100 mmHg. The systolic BP on admission was significantly lower (p less than 0.001) and the heart rate (HR) higher (p less than 0.001) than when the patients left the ward. Apart from an increased HR (greater than or equal to 90 beats/min), which was present in 73% of the cases, the most characteristic ECG change was a QRS prolongation (greater than or equal to 0.11 sec), this being found in 42% of the cases. About the same proportion displayed a QT prolongation and 28% had a prolonged PQ time. The mean of the QRS times was 0.11 sec. Unlike the QT time, the QRS time was not correlated to HR. Statistical analysis of the material with regard to clinical variables (dose of TCA, BP, coma duration, etc.) showed that the QRS time was closely related to the severity of poisoning. Five patients (3) died, all of whom already on admission demonstrated advanced ECG changes with arrhythmias and a mean QRS time of 0.19 sec. Excluding dibenzepine poisonings (4 cases, all fatal), the mortality rate was 0.7%. The importance of high initial preparedness for cardiac complications is pointed out, as is the value of the QRS time as a guide to the severity of poisoning.