Little is known about the expression of growth factors and their receptors in pituitary tumors or the relationship of growth factors to pituitary neoplasia. Platelet-derived growth factor (PDGF) is a potent mitogen that has been postulated to stimulate tumor growth through autocrine and/or paracrine loops in a number of human tumors. In the present study we demonstrate messenger ribonucleic acid expression of the PDGF subunits and receptors in a variety of human pituitary adenomas and in a normal human anterior pituitary gland. Northern blot analysis performed on 34 pituitary adenomas showed that all tumors expressed the PDGF-A and PDGF-B subunits, the majority (94%) expressed the PDGF-beta receptor, and a subset (44%) expressed the PDGF-alpha receptor. The normal anterior pituitary studied expressed all of the PDGF subunits and receptor subunits. Clinically, there was no correlation between expression of the PDGF subunits or receptors and tumor size or with invasion into adjacent structures (cavernous sinus, sphenoid sinus, or clivus). A higher proportion of the endocrinologically active adenomas expressed the PDGF-alpha receptor (5 of 8) compared to the endocrine inactive tumors (10 of 26). The function of PDGF in the pituitary is currently not known. The finding that PDGF subunit and receptor messenger ribonucleic acids are coexpressed in pituitary adenomas and normal anterior pituitary suggests that autocrine and/or paracrine loops involving PDGF may exist in pituitary adenomas and normal anterior pituitary.