In a recent investigation of hepatitis in Bangladesh, the sera from 74 adult patients (aged 15-67 years) who had been clinically diagnosed as cases of sporadic acute hepatitis were collected at various hospitals in and around Dhaka. Five cases were positive for IgM antibody against the hepatitis A virus and 30 were positive both for the surface antigen of the hepatitis B virus (HBV) and for IgM antibody against the HBV core (HBc). The six cases found positive for antibodies against the hepatitis D virus were all also positive for the HBV surface antigen but negative for anti-HBc IgM. Thirteen patients harboured hepatitis C virus RNA and 29 were positive for IgM antibody against the hepatitis E virus (HEV). There were 14 non-A-to-E subjects, whose illness was of unknown aetiology. Of the 83 infections with hepatitis viruses detected in the other 60 patients, 6%, 36%, 16%, 7% and 35% were of types A, B, C, D and E, respectively. Each of 28 of the patients (47% of those confirmed to have viral hepatitis) had concomitant infection with more than one type of hepatitis virus. The predominance of HBV and HEV infections and the high prevalence of multiple infection seen among these Bangladeshi cases have not been observed among hepatitis cases in developed countries.