Vienna suffered an epidemic of heroin abuse in recent years, with drug-deaths due to opioids increasing from 62 in 1991 to 143 in 1993. The aim of this study was to make observations about illicit opioid-use with the ambulance service as a data source. From June 1994 to August 1995, the structured run records of the ambulance service were reviewed. Those with a presumptive diagnosis of "heroin or opiate" overdose were collected, characteristics of emergencies and patients were analyzed. The run records demonstrated a large number of non-fatal emergencies due to opioids, involving 528 men and 179 women in 1087 emergencies. These emergencies were on the average 6.8 times as prevalent as drug-fatalities. A group of 189 persons could be identified, who caused 52.2% of all emergencies and showed a threefold mortality rate during the observation period. In Vienna, the records of the municipal ambulance service provided valuable insights on opioid-abuse. We suggest local analysis of non-fatal emergencies due to opioids, as this might lead to a new source of information on illicit abuse of these drugs.