The ability to measure changes in brain levels of corticotropin-releasing factor (CRF) is an important step toward understanding the role of this neuropeptide in mood states. Here, we report for the first time that the protein (Western) immunoblot assay can be used to detect and quantify CRF (4.7 kDa) from the rat brain. Intracerebroventricular (ICV) injections of the neuronal transport-inhibitor colchicine (0, 7.5, 15 and 75 microg) produced a dose-dependent increase in CRF levels within the paraventricular nucleus (PVN) of the hypothalamus with a concomitant and dose-dependent decrease in CRF levels within the median eminence (ME). These data provide a positive validation for the use of the immunoblot assay to detect treatment-induced changes in brain CRF levels.