To complement investigations of hepatitis B virus infection in hepatocellular carcinoma associated with cirrhosis, we studied hepatitis B virus infection in 137 hepatoma patients without cirrhosis. Ninety-five were from the U.K. (where the prevalence of hepatitis B virus markers is very low) and 42 were from overseas. Of these 137 patients, seven (5%) were hepatitis B surface antigen seropositive. None of the hepatitis B surface antigen positive patients had any recognisable risk factors other than birth in an area of high hepatitis B virus prevalence in four of the patients. Of the 95 U.K. patients three (3%) were hepatitis B surface antigen positive as compared to a carriage rate of less than 0.1% in the normal population. The frequency of antibodies to hepatitis B surface and core antigens alone (both 7.5%) was also higher than that seen in the normal U.K. population (2.4%). Histological examination of the non-tumorous liver showed fine fibrous septa in three patients, more extensive subcapsular scars in one, chronic persistent hepatitis in two and non-specific inflammation in one. On immunohistochemical examination five patients had hepatitis B surface antigen (but not core antigen) detectable in the non-tumorous liver tissue. Hepatitis B virus infection appears to be a small, but significant, risk factor for the development of hepatoma in the non-cirrhotic group.