Cerebrocyte antigens of human embryo and indirect assay of solid phase ELISA were applied to measure concentrations of IgG subunit of serum anti-brain antibody (ABA) and other immunological indexes in 110 epileptics, 36 neurasthenic patients and 52 normal individuals. The results showed that the levels and abnormal rate of serum ABA in epileptic patients was much higher than those of controls (P less than 0.001). However there was no difference among the controls (P greater than 0.05). It suggested that epilepsy might be caused by certain factors resulting in the exposure of the sealed brain antigen which in turn stimulates ABA production and autoimmune responses. The serum level of ABA was correlated with that of serum IgG and IgA (P less than 0.05), but not with age, duration of disease, seizure types and the use or nonuse of anticonvulsive drugs (P greater than 0.05).