Circulating immune complexes were investigated by polyethilene-glycol precipitation in the serum of 101 neurological patients from four months to 15 years old. The test was positive in 21 cases (20.7%) and 24 normal controls were negative. The polyethilene-glycol positive group had a lower seric C'3 than negative group [p < 0.02]. The highest positivity was found in meningoencephalitic infections with sequelae [6/6: 100%] and in cerebral atrophy or very important mental deficiency [11/30: 37%]. The polyethilene-glycol test was not correlated with seric IgG levels, neither in positive nor in negative groups. All patients were receiving anticonvulsivant treatment. The detection of circulating immune complexes may be the result of either brain tissue injury or of another immunological disturb found in epilepsy. There was no relationship between seric immunocomplexes and severity of epileptic disorders and it is not likely that they have any influence over seizures. The role played by anticonvulsivant drugs remains uncleared and further studies are needed.