By utilizing certain specific substrates for UGTs, we initially demonstrated that catalytic activities of UGT1A, UGT1A1, UGT1A4, UGT1A9 and UGT2B7 were significantly decreased in the tumor tissues in HBV-positive HCC patients (Figs 1 and 2A–6A). Here, UGT1A4 is linked to hepatocellular carcinoma.