The peripheral blood lymphocyte subsets, serum immunoglobulins (Ig A, G, M), and C3 and C4 complement protein concentrations were determined in 40 healthy subjects, 30 phenytoin-treated, 22 carbamazepine-treated and 38 untreated epileptic patients. The levels of B-lymphocytes, IgM and C3 complement proteins were found to be significantly higher in untreated epileptics than in healthy controls (P<0.01, P<0.02 and P<0.05, respectively). The absolute number of B-lymphocytes appeared to be unaffected by phenytoin or carbamazepine treatment; however, IgM levels were significantly lower in carbamazepine-treated patients than both epileptic (P<0.01) and healthy (P<0.05) controls. Phenytoin-treated patients had a significant reduction in the mean IgA and IgG levels compared to healthy and epileptic controls (P<0.05). With both drug treatments, significantly lower T-suppressor lymphocyte counts and thus higher T-helper to T-suppressor lymphocyte ratios were observed with respect to healthy and epileptic controls. Our results demonstrate that while phenytoin decreases serum IgA and IgG levels, carbamazepine reduces IgM levels significantly, and untreated epileptics show immune profiles significantly different to those of healthy subjects, suggesting that epilepsy per se may be associated with certain immune aberrations induced by antiepileptic drugs.