The human pregnane X receptor (hPXR) plays a key role in the regulation of both drug metabolism and efflux by inducing the expression of CYP3A4 and MDR1 gene. Using reverse transcription-polymerase chain reaction (RT-PCR) analysis, we identified seven novel splicing variants of hPXR in tissue from a single human liver. The expression of hPXR-related transcripts in the liver samples of 15 Caucasian individuals was subsequently determined by RT-PCR assays. The pattern of expression levels of these transcripts varied among liver samples. These results suggest that the hPXR is expressed as several different transcripts in liver tissues, apparently due to alternative as well as defective gene splicing. Furthermore, because this study provides the possibility of interindividual differences in hPXR transcript profiles, these alternative splicings for hPXR may largely contribute to the interindividual variability in CYP3A4 and beta-glycoprotein induction. (C) 2002 Elsevier Science (USA). All rights reserved.