Serum immunoglobulin levels A, G, M, D have been studied in 902 patients suffering from allergic or non-allergic asthma, rhinitis and cough or various combinations of these disorders. In addition, a control group of asymptomatic persons was included. Serum IgA and IgD levels were significantly lower in both the allergic and non allergic groups of patients as compared to the control group, indicating that this decrease is a common feature for all patient groups studies. Serum IgA was significantly increased in amount in smokers. Serum IgA and IgG levels increased significantly with age. Females showed significantly higher serum IgM levels as compared to males. Atopic eczema did not seem to influence the serum level of immunoglobulin classes A, G, M or D.