Sera from 80 Malaysians with confirmed hepatocellular carcinoma were tested for five markers of the hepatitis B virus, anti-HCV and anti-HDV by enzyme immunoassay, and alpha fetoprotein (AFP) was measured by radioimmunoassay. Of the patients, 98.8% had evidence of HBV infection and 75% were positive for HBsAg--which latter correlated with AFP raised above cut-off values of 500 ng/ml (P = 0.0001) and 200 ng/ml (P = 0.005). Males correlated significantly with the presence of HBsAg (P = 0.002). Thirty-one per cent of HBsAg positive patients were also positive for HBeAg and 74% for anti-HBe. Twenty per cent of the cases were concurrently positive for both HBsAg and anti-HBs. Six of 70 (8.6%) patients were positive for anti-HCV, of whom four were also positive for HBsAg. None of 67 patients tested for anti-HDV were positive. The results strongly indicate an important aetiological role for hepatitis B virus in causation of hepatocellular carcinoma among Malaysians.