In a study undertaken to determine compliance with Universal Precautions, we observed 129 personnel performing 1,274 interventions on 151 consecutive critically ill and injured patients in an emergency department setting in July 1988. Barrier precautions were fully adhered to 44.0% of the time. During interventions in patients with profuse bleeding, adherence was only 19.5% in contrast to 44.7% for those who were not bleeding. Adherence was 56.4% during minor interventions but only 16.7% during major procedures. Adherence rates varied among health care providers: residents, 58%; emergency staff physicians, 38%; consultant physicians, 43%; emergency nursing staff, 44%; paramedics, 8%; radiology technicians, 14%; and housekeeping, 91%. In a follow up questionnaire that ascertained reasons for lack of compliance, 47% of providers indicated that there was not always sufficient time to put on protective material, 33% felt that precautions interfered with skillful performance of procedures, and 23% stated that materials were uncomfortable. Only 2.7% felt that Universal Precautions did not work. Since there is no proven postexposure prophylaxis for human immunodeficiency virus, Universal Precautions must be rigorously followed until such time as they are shown not to be effective or an alternate approach is developed. Strategies to improve compliance and improvements in barrier technology need to be developed.