The concentrations of immunoglobulin A (IgA) and phenytoin were determined in 36 epileptic children with a mean age of 11 years. There was a good correlation between the plasma and saliva concentrations of phenytoin (r = 0.94). The concentration of phenytoin and IgA showed little variation during the dosage interval. The phenytoin treated children did not differ with respect to the concentrations of IgA in saliva in comparison to the controls.