To assess the prevalence and utility of citizen cardiopulmonary resuscitation (CPR) training, a systematic population-based sample of Minneapolis-St. Paul area adults, age 25-74 years, was interviewed in 1980-81. Twenty-three per cent were CPR trained. Of these, 13 per cent have encountered out-of-hospital cardiac arrests and 38 per cent reported using their skills in such an emergency. Most of those performing out-of-hospital CPR (59 per cent) were health professionals. Only 19 per cent of trainees have maintained their certification by retraining within one year.