Serum immunoglobulin G, A and M concentrations and their respective kappa/lambda (kappa/lambda) light chain ratios were studied in 26 children with epilepsy. Fifteen had cryptogenic West syndrome or Lennox-Gastaut syndrome and 11 had other forms of childhood epilepsy. The results were compared to the data of a reference group of healthy children. The mean serum IgG and IgM concentrations were respectively 2.2 g/l (P = 0.007) and 0.4 g/l (P = 0.016) higher in the 26 children with epilepsy compared to the reference group. The kappa/lambda ratios of total serum immunoglobulins, IgG and IgM were respectively 0.10 (P = 0.057), 0.20 (P = 0.001) and 0.14 (P = 0.005) lower in the children with epilepsy than in the reference group. IgA concentration and IgA kappa/lambda ratio were not affected. There were no significant differences between the kappa/lambda ratios of the West and Lennox-Gastaut epilepsy and the other types of childhood epilepsies. The results are further evidence of reciprocal interaction between the nervous system and the immune system in childhood epilepsy.