Immunoglobulin E was measured in concentrated cerebrospinal fluid (CSF) of controls and patients with various neurological disorders, including multiple sclerosis (MS). The radioimmunoaasay method was used for IgE and the single radial immunodiffusion method was used for other immunoglobulins. IgE in CSF was able to quantify in 86.4 % of 118 cases, and then, it is thought that there is quantitative IgE component in normal CSF. In controls (N=23) IgE contents ranged from 0.03 to 0.71 U/ml (M: 0.28 U/ml). IgE /100mg of total protein ratio in CSF ranged from 0.06 to 1.52 (M: 0.61 ). Then, it is suspected that normal value of IgE and IgE % is below 0.8 U/ml and 1.6. The CSF/serum ratio of IgE was about 0.1 % (0.08-0.12 % ). This value is larger than that of IgM, and smaller than that of IgA and suggests immunoglobulin permeability through the blood-brain-CSF barrier in reverse proportion to molecular weight. In pathological CSF, the increase of IgE was related to the increase of total protein, IgG, IgA and IgM levels but IgD. IgE level was increased in 19 of 84 cases (22.6 % ), especially high IgE level was seen in acute inflammatory diseases of central nervous system but in chronic disorders (for example dementia paralytica). Otherwise, polyradiculoneuritis and diseases with abnormality of CSF dynamics or brain atrophy, revealed the tendency of high IgE levels. In these disorders, the increase of IgE was parallel with total protein level, IgG and other immunoglobulins in most cases. The incidence of high IgE level in MS was 3 of 15 cases, but these increases of IgE were not corelated with abnormalities of other components in CSF and it was revealed the possibility of another pathophysiological process of IgE from IgG and other immunoglobulins in central nervous system. No relationship was present between the incidence of high CSF IgE level and various factors such as clinical stage, suspected lesion and severity of disturbance in MS.