Blood exposures are increasingly recognized as a risk for health care workers in the operating room. Trained circulating nurses supervised by site coordinators queried surgical team members about blood contact and collected data on 8502 surgical procedures from seven community and two university hospitals in 1992. Blood contact occurred during 864 cases (10.2% case-contact rate) in 1054 health care workers (12.4% person-contact rate). The parenteral exposure (punctures or cuts, mucous membranes, nonintact skin) rate was 2.2% and the cutaneous exposure (intact skin) rate was 10.2%. Blood contacts were twice as likely to be parenteral among surgeons as among other operating room personnel (odds ratio, 2.0; 95% confidence interval, 1.4 to 2.9). Of cutaneous exposures, 46.9% were from unknown sources or were surprise spatters. Logistic regression analyses indicated that risk factors associated with any blood contact (parenteral or cutaneous) were length of procedure (odds ratio, 1.51; 95% confidence interval, 1.46 to 1.56), emergency versus scheduled status (odds ratio, 1.44; 95% confidence interval, 1.21 to 1.66), selected surgical services, and the hospital. Logistic regression analyses of parenteral exposures, as compared with cases in which no contact occurred, indicated that risk factors were length (odds ratio, 1.39; 95% confidence interval, 1.31 to 1.47), thoracic surgery (odds ratio, 2.79; 95% confidence interval, 2.18 to 3.40), and university hospital versus community (odds ratio, 2.26; 95% confidence interval, 1.89 to 2.63). Parenteral exposures are clear risks to health care workers; however, it is also important to study all contact with blood in the operating room to appreciate potential risks and develop appropriate intervention strategies.