GHRH is produced in a variety of extrahypothalamic tissues, including some neoplasms. We have previously reported that GHRH antagonists can inhibit the growth of various human cancers xenografted into nude mice. These observations suggest that locally produced GHRH might directly affect tumor cell proliferation. To investigate this possibility, we have examined the local production of GHRH in human endometrial, ovarian, and breast cancers obtained after surgery or grown in nude mice as xenografts. We have also examined whether the GHRH produced in these tumors is biologically active. RT-PCR and Southern blotting showed expression of messenger ribonucleic acid for GHRH in 17 of 22 endometrial and 17 of 22 ovarian cancer specimens and in all of the human endometrial, ovarian, and breast cancer xenografts studied. Acid extracts of endometrial cancer specimens and breast cancer xenografts that expressed the GHRH gene contained immunoreactive GHRH peptide, as assessed by RIA for GHRH. The level of immunoreactive GHRH detected was equivalent to 2.7-6.4 ng GHRH-(1-29)/g tissue. Purified extract from one of these tumor samples induced a powerful stimulation of GH release from rat pituitary cells. The presence of biologically and immunologically active GHRH and messenger ribonucleic acid for GHRH in human breast, endometrial, and ovarian cancers supports the hypothesis that locally produced GHRH may play a role in the proliferation of these tumors.