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INTRODUCTION SERUM immunoglobulin determinations are of potential value to clinicians in evaluating immunoinflammatory diseases and in the detection and characterization of immunodeficiency or hypergammaglobulinemia. Certain biologic variables affect concentrations of serum immunoglobulins [l-4] and must be considered in interpretation of specific levels in any individual patient. Efforts by different authors to determine general norms of immunoglobulin concentrations and lifetime trends have diverged considerably. The present study of sex and age effects on serum concentrations of JgG, IgA, and IgM is based on data from a large unselected group of subjects from a single community. Study group MATERIALS AND METHODS 3213 consecutive sera were obtained in a community health study in Tecumseh, Michigan (42"N latitude, 83"W longitude) from May 1968 to April 1969. All individuals were of the white race. Sera were divided aseptically into aliquots and stored at 4°C; they were either assayed within a week or frozen at-70°C until analysis. Preparation of puriJed immunoglobulins and antisera TgG was prepared from Cohn Fraction II (American Red Cross, Bethesda, Md.) by DEAE-cellulose (Carl Schleicher & Schuell Co., Keen, N.H.) chromatography with 0.0175 M phosphate buffer, pH 6.3 [5]. IgA was prepared from myeloma sera by