The incidence, etiology and risk factors of posttransfusion (PT) hepatitis were evaluated in a prospective study of 297 consecutive open-heart surgery patients. PT hepatitis occurred in 63 (21.2%) patients with a significantly higher hepatitis attack rate in 51 recipients of commercial clotting factor concentrates (56.8%) compared to 246 recipients of blood units from single volunteer donors (13.8% p<0.001). Among the concentrates, Prothrombin- complex showed the highest relative hepatitis risk (24) while in patients receiving only blood, the incidence PT hepatitis was correlated with the blood volume transfused. Of the 63 patients with PT hepatitis, 2 (3%) had hepatitis B, 8 (13%) showed evidence of cytomegalovirus infection and 53 (84%) had non-A, non-B hepatitis. These results show that in Italy, as elsewhere, non-A, non-B PT hepatitis is frequent, particularly when commercial blood products are used.