All resuscitation attempts outside hospital attended by the Auckland life support unit ambulances during 1983 were reviewed. There were 405 attempted resuscitations during the 12 month period. Of the 344 patients who arrested before the life support unit arrived, 189 (55%) had cardiopulmonary resuscitation initiated by bystanders and 34 (10%) by conventional ambulance personnel. Sixty one patients suffered their arrest after the arrival of the life support unit. One hundred and ninety two patients (47% of the total 405 patients) died at the scene of collapse, 95 patients (24%) died in accident and emergency departments and 46 (11%) died in hospital. Eighteen of the 213 patients successfully resuscitated and transported to hospital had complications related to cardiopulmonary resuscitation. Of the 72 patients discharged, 65 (90%) were alive one year after discharge. Of all patients in whom resuscitation was attempted, 75% were males. This male predominance was present in all age groups and disease categories except subarachnoid haemorrhage and stroke. Myocardial infarction and other ischaemic heart disease accounted for the great majority of cases, followed by asthma and a variety of other conditions. Below 30 years of age the causes of collapse were predominantly noncardiac, and with age increasing above 30 years there was increasing likelihood of a cardiac cause for the collapse.