Immunoglobulin concentrations were determined in the sera and nasal washes of 111 patients with chronic obstructive pulmonary disease who were 45 to 60 years of age and in 111 control subjects matched with the patients for age, sex, occupation, and smoking history who demonstrated normal 1-sec forced expiratory volume. Serum IgA, IgM, IgG, nad IgE were not significantly different in the 2 groups. Serum IgD was significantly higher in subjects with chronic obstructive pulmonary disease. Nasal wash IgD and IgM, expressed as percentages of total protein, were higher in index cases, but nasal wash IgA and IgG were comparable in both groups. The finding of relatively high concentrations of IgA, expressed as fractions of total protein, in respiratory secretions compared to serum is consistent with earlier findings that IgA is actively secreted from the respiratory epithelium and is not deficient locally in subjects with chronic obstructive pulmonary disease. In contrast, IgM and IgG expressed as proportions of total protein were consistently higher in sera than secretions. The IgE in nasal secretions was detected so seldom in this study that too few matched pairs were available for statistical analysis. The higher concentration of IgD in the serum and nasal secretions of patients with chronic obstructive pulmonary disease compared with their matched pairs and the associated higher frequency of low IgD in control subjects suggests that low IgD may be protective against the development of chronic obstructive pulmonary disease. Further studies on the biologic role of IgD may provide better understanding of these findings.