Catecholamine concentrations of the spleen were studied with neurochemical techniques in rats injected with myelin basic protein to produce an experimental allergic encephalomyelitis EAE). Thirteen to 14 days postinoculation the affected rats showed peak clinical signs of weakness, especially in the lower extremities. Resolution of the disease then progressed rapidly with full clinical recovery at day 21. Splenic concentrations of norepinephrine (NE), 3,4- dihydroxyphenylalanine (DOPA), epinephrine (EPI) and 3,4-dihydroxyphenylethylamine (DA) were determined by HPLC with electrochemical detection. DOPA concentrations were significantly increased (+62%) while DA concentrations were decreased (-29%) in the EAE rats on day 14 postinoculation. NE and EPI concentrations tended to be elevated in the EAE group, but this was not statistically significant. No differences in splenic catecholamines were detected on day 7 and 52 postinoculation between EAE and control animals. There results indicate that changes in the metabolic pathways of splenic catecholamines occur at the peak of the clinical symptoms of EAE; the increase in DOPA and the decrease in DA concentrations suggest that the activity of DOPA-decarboxylase or its co-factor is altered. © 1987.