Total IgG and IgG subclasses were studied in 34 patients with primary Sjögren's syndrome and 4 with hypergammaglobulinemic purpura. Total IgG was elevated in 30/34 patients with Sjögren's syndrome. IgG1 increase was responsible for the main part of total IgG increase, contrasting with low levels of IgG2. The difference in IgG1/IgG2 ratio between 38 patients as a group and 40 normal controls was statistically highly significant, but was not seen in all patients. Six patients had markedly low levels of IgG2, but only two had severe repeated respiratory infections. These observations probably reflect selective autoantibody restriction to the IgG1 subclass. We conclude that patients with Sjögren's syndrome may be IgG2 subclass deficient despite elevated levels of total IgG, but also that such deficiency in most instances does not cause a tendency to infections. IgG subclass analysis may be of value to characterize polyclonal IgG increase, since IgG1 subclass predominance often indicates autoimmune disease.