Symptoms of respiratory tract disease were recorded for half a year in 32 epileptic patients receiving phenytoin, and in 25 controls. There were 16 patients with normal IgA concentration in serum and nasal secretion, and 16 with a reduced concentration of IgA either in serum or in nasal secretion, or in both. Both groups of patients had significantly more frequent respiratory symptoms than did the controls (P less than 0.01). There was no difference when the patient group with decreased IgA concentrations was compared to that with normal IgA levels. All the four patients with IgA deficiency both in serum and nasal secretion had, however, more frequent symptoms than any of the controls. There was no difference regarding respiratory tract disease in patients taking phenytoin only, compared to those combining phenytoin and other anticonvulsants. IgG and IgM levels in nasal secretion showed no direct relationship to the frequency of respiratory symptoms.