Vitamin A is required for normal growth and development, and retinoic acid (RA) may be the active metabolite in this process. Recent evidence indicates that RA acts through binding to a nuclear receptor which belongs to the steroid/thyroid hormone receptor superfamily. The receptors seem to associate with hormone-response elements in the target genes resulting in the activation (or inhibition) of transcription. Although no interaction of RA-receptor complex with specific DNA sequences has yet been reported, the homology of the different receptors suggests their mechanisms of action are similar. We therefore examined whether the effects of RA on growth could be related to changes in the expression of the growth hormone gene which is known to be transcriptionally regulated by both thyroid and glucocorticoid hormones. Our results show that RA controls growth hormone production in pituitary GH1 cells and that its effect is synergistic with that caused by these hormones.