We have used mRNA diVerential display to compare gene expression in normal and GH receptor-deficient dwarf chickens, and report here the characterization of one diVerentially expressed gene, which shows significant sequence identity to the sulfotransferase gene family. Partial cDNA clones were isolated from a chicken liver cDNA library and an additional sequence was obtained using 5* rapid amplification of cDNA ends. A complete cDNA probe hybridizes to three transcripts (2·4, 2·0 and 1·45 kb) on Northern blots of chicken liver RNA, which diVer in the length of the 3* untranslated region. All three transcripts are expressed at higher levels in normal vs dwarf chickens, as expected for a GH-regulated gene. The expression of this sulfotransferase mRNA was also detected in skeletal muscle, but not other tissues. The administration of GH to chickens increased the hepatic expression within 1 h, suggesting this sulfotransferase could be directly regulated by GH. Sulfotransferase activity, using estradiol or corticosterone as substrate, is detected in cells transfected with an expression vector containing the full-length cDNA. The sequence of this sulfotransferase does not show significant similarity with any subfamily of the sulfotransferases and its endogenous substrate is presently unknown. However, we speculate that GH activation of sulfotransferase activity could play a role in reducing concentrations of growth-antagonistic steroid hormones in GH target tissues. These results demonstrate the usefulness of diVerential display in this model system to identify genes that play a role in mediating GH action.