Titers of anti-keratin antibodies (AKA) involving IgG and IgM fractions were determined by a solid-phase enzyme-linked immunsorbent assay (ELISA) and were found to be significantly higher on average in patients with pustulosis palmaris et plantaris (PPP) than in normal controls. Positive rates of IgG-AKA and IgM-AKA in sera of PPP patients were 50% and 66%, respectively. Following tonsillectomies, patients with high IgM-AKA titers that decreased after surgery were found to benefit by a marked improvement in their skin lesions. There was a close relationship between the degree of this improvement in the skin lesions and the changes in IgM-AKA titers after the operation. These results suggest that PPP may be a tonsil-related immunological skin disease.