Corticotropin-releasing factor (CRF) initiates stress-induced immunosuppression via the hypothalamic-pituitary-adrenal axis. CRF has also been shown to have direct stimulatory and suppressive effects on immune cells. We have previously detected immunoreactive and bioactive CRF in the rat spleen and thymus. To determine if CRF is synthesized in these tissues, we analyzed rat spleen and thymus for the presence of CRF mRNA. RNA was reverse transcribed, and the resulting cDNA was amplified by the polymerase chain reaction with CRF gene-specific oligonucleotide primers. After Southern blotting and hybridization with an internal CRF gene probe, a product of the expected size was detected in the spleen, thymus, and hypothalamus (positive control) but not in liver or kidney (negative controls), indicating that CRF is synthesized in the spleen and thymus. Furthermore, CRF could be secreted from splenic and thymic adherent cells in culture. Secretion increased severalfold in response to nordihydroguaiaretic acid (NDGA), a lipoxygenase pathway inhibitor, whereas interleukin 1 had no effect, suggesting that regulation of CRF secretion may differ from that in the hypothalamus. CRF mRNA was detected in NDGA-stimulated thymic adherent cells and in both control and NDGA-stimulated splenic nonadherent cells. The finding that CRF is synthesized in the spleen and thymus suggests that locally synthesized "immune" CRF, acting as an autocrine or paracrine cytokine, may have direct regulatory effects on immune function.