Using a cDNA clone derived from the rat Glutathione S-Transferase P (GST-P) gene, we have investigated homologous transcripts in a range of normal and malignant human tissues. A major transcript, of 0.75 Kb, representing human GST-pi mRNA, was present in total RNA purified from peripheral white blood cells, bladder, ureteric and prostate tissues. In total RNA derived from histopathologically benign/normal tissues, peripheral leucocytes and from hyperplastic and malignant prostates, levels of the mature transcript varied by less than 1.5-fold (n = 70). In contrast, levels of transcript were significantly elevated (up to 16-fold) in total RNA derived from bladder and ureteric carcinomas, with the highest levels of elevation approaching those previously found only for the GST-P gene in experimentally induced rodent hepatocellular carcinomas. A wide range of stage and grade of tumour has been investigated (pT1 to pT4; G1 to G3, respectively), suggesting that the transcriptional activation of the GST-pi gene is a characteristic common to many bladder/ureteric carcinomas in man.