Human growth hormone (hGH) gene expression and regulation by thyroid and glucocorticoid hormones were examined after its stable introduction into rat anterior pituitary tumor cells. Transcripts from the hGH gene were correctly initiated and could be positively regulated by glucocorticoids. In contrast to the endogenous rat GH gene and a transfected, modified rat GH gene, the hGH gene was negatively regulated by triiodothyronine. Analysis of hGH gene 5'-flanking deletions indicated that a distal regulatory element is required for efficient transcription. Thus promoter, glucocorticoid, and thyroid hormone control elements are present on the transfected hGH gene, whose expression may be negatively controlled by thyroid hormone.