A fluorescein-conjugated bioactive analog of corticotropin-releasing factor (CRF) was synthesized and used to label cells that have high affinity CRF-binding sites. Of cultured bovine anterior pituitary cells, 6.1 +/- 0.6% were visible by fluorescence microscopy after incubation with the analog. Fluorescence was eliminated by coincubation with a 200-fold excess of unlabeled CRF. Treatment with dexamethasone (10(-9)-10(-7) M) decreased visible fluorescence in a dose-dependent manner. These results demonstrate the utility of a fluorescent CRF analog for identification of cells with specific CRF-binding sites and suggest that binding of CRF to anterior pituitary cells is altered by glucocorticoids.