The ability of the differentiated human intestinal cell line, Caco-2, to glucuronidate various endobiotic and xenobiotic molecules was investigated. Glucuronidation of hydroxylated or carboxylic acid compounds such as 1-naphthol, thymol, androsterone, estriol, hyodeoxycholic acid, lithocholic acid, chloramphenicol, paracetamol and morphine could be determined in microsomal fractions of Caco-2 cells. The activity toward 1-naphthol was the highest glucuronidation activity measured in Caco-2 cells. This activity was specifically increased four-fold upon addition of beta-naphthoflavone into culture medium but not by rifampicine or clofibrate and was related to a biosynthesis of UDP-glucuronosyltransferase 1*6 (UGT1*6). alpha-Naphthoflavone did not affect the inducing property of beta-naphthoflavone. 7-Ethoxyresorufin-O-dealkylation activity, supported by cytochrome P4501A1, was induced more than 1000-times in Caco-2 cells by beta-naphthoflavone treatment, and this effect was partially abolished by alpha-naphthoflavone treatment. The results suggest that several isoforms, including UGT1*6, are expressed in Caco-2 cells.