One hundred and thirty adults with viral hepatitis were hospitalized in the Department of Hepatology-Gastroenterology at the Hospital Salpètrière between October 1984 and October 1986. Eighty had acute hepatitis and 50 suffered from chronic hepatitis. Among the former, 15 had hepatitis A, 40 had hepatitis B and/or delta and 25 had non A-non B hepatitis. The latter group was divided into 32 hepatitis B and/or delta and 18 non A-non B. The results of clinical, biological, serological and histological analyses were comparable to those reported in the literature for hepatitis A and B. Hepatitis non A-non B was more prevalent in males (72%). This predominance seems to be associated with the high number of heart transplant patients (12, 11 of them were men) in our study population. A liver biopsy was performed on 19 out of the 25 acute and on 32 of the chronic non A-non B hepatitis patients. Persistent chronic hepatitis was the most commonly found lesion. Transfusion was implicated in 53.8% of the patients, drug addiction in 18.6% of the cases and intramuscular injection or acupuncture in 5% of them. No risk factor was found in 23.2% of the patients. Seventy-two percent of the acute non A-non B hepatitis cases evolved towards a chronic form. We have attempted to find the factors involved in progression to chronicity. No correlation was found for age or the means of contamination. In contrast, immunodepression was significantly correlated. This study reflects the prevalence of non A-non B hepatitis infection post-transfusion in a hospitalized population including many transplant recipients.