Tissue-specific expression of human UGT1A6, a UDP-glucuronosyltransferase isoform conjugating a wide variety of planar phenols, has been studied using a reverse transcriptase-polymerase chain reaction. Use of intron-overlapping forward and reverse primers from exon 1 and 2 and of a "hot start" modification led to selective amplification of a UGT1A6 mRNA fragment. In addition, homologous competitor mRNA was synthesized, reverse transcribed, and coamplified to allow quantitation of UGT1A6 mRNA. Using these methods UGT1A6 mRNA could be demonstrated in liver, kidney, duodenum, and lung. Cell-specific regulation of UGT1A6 by TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) was studied in various cell systems. TCDD induction was found in the human colon carcinoma cell line Caco-2 and in hepatocyte primary cultures. In contrast, in lung carcinoma A549 cells this isoform was constitutively expressed and not induced by TCDD.