Rats were given intraventricular (ivt) injections of various doses (50-400 micrograms, hydrobromide salt) of 6-hydroxydopamine (6-OHDA) and killed 1, 3 or 6 days later. Brains were removed, dissected into 11 regions, and the thyrotropin-releasing hormone (TRH) content of each region was measured by radioimmunoassay. 6-OHDA (400 micrograms) caused significant elevations in the TRH content of 6 regions: olfactory bulb, anterior cortex, brainstem, posterior cortex, hippocampus, and amygdala-piriform cortex. The magnitude of these increases ranged from 59% in olfactory bulb to 497% in hippocampus and was, in all cases, greatest at 3 days. These results suggest that the TRH content of certain brain regions may be regulated by catecholamine neurotransmitters.