Forty neurosurgical, artificially ventilated patients were examined. Twenty of them had been diagnosed as brain dead, while twenty non-brain-dead patients served as a control group. From a surface ECG taken over a period of five minutes the mean heart rate and various indices of heart rate variability (HRV) were determined with the help of a special computer program (ProSciCard, Medisyt, Germany). The heart rate of the brain dead was significantly higher than that of the control patients. By contrast, all parameters of HRV were drastically reduced in the brain dead individuals compared to the controls. The results show that a significant change in the course of heart rate occurs after manifestation of brain death. This would appear to be the result of the elimination of all vegetative impulses derived from the brainstem. Computer-aided, the changes can be quantified in a simple way. The method could therefore be useful in brain death diagnosis.