The central nervous system (CNS) of guinea pigs undergoing acute experimental allergic encephalomyelitis (EAE) induced by whole CNS shows a characteristic progression of proton NMR relaxation times that correlates with pathologic features of the disease. Specifically, T1 was prolonged during meningeal infiltration and perivascular inflammation. T2 was increased with demyelination. Both proton T1 and T2 values, however, were normalized in active lesions containing an extensive cellular response (encephalitis, myelitis).