The impact of the introduction of Medicare in Quebec on hospital emergency room services was examined in Metropolitan Montreal. After Medicare, the emergency room visit rate increased 14 per cent per year compared to a 7 per cent per year increase in the five years preceding Medicare. The outpatient clinic visit rate continued an upward trend (4 per cent per year). In six of the hospitals selected for more detailed studies, patient interviews revealed that before Medicare 33 per cent of emergency room attenders attempted to contact a physician before reporting to the emergency room and 63 per cent were successful in speaking to the physician. After Medicare, 39 per cent attempted but only 38 per cent were successful. Before Medicare, 47 per cent of patients said that their usual source of care was a private physician, and only 17 per cent usually sought care in the emergency room. After Medicare 58 per cent reported a private physician and 31 per cent the emergency room. These findings together with the increased population density of physicians and increased annual number of physician visits per person suggest that there has been a substantial rise in demand from the public for medical care of which one important early manifestation is an increased reliance on emergency rooms.