The control group was made up of 79 prospectively enrolled healthy adult volunteers, 40 of whom (mean age, 29.5 years) were studied to establish a criterion for a normal response to the pneumococcal vaccine, and 59 of whom (mean age, 32 years) to establish a criterion for a normal response to the Hib conjugate vaccine, as we published previously.12,22 Twenty of the 79 healthy adults received both vaccines.22 None had a history of recurrent or severe infections, acute or chronic pulmonary disease, primary or secondary immunodeficiency, autoimmune systemic disorder, or any disease or intake of drugs that might affect antibody production. They had not suffered any infection during the month preceding the vaccination. Forced spirometry, WBC count, creatinine, transaminases, and serum total Ig levels were within normal range. An arbitrary value, corresponding to the lower limit of the two-tailed 90% probability interval of postimmunization specific IgG of the healthy adults, was defined as the minimum significant increase for an adequate response. All subjects showing an increase in specific antibody titers equal to or greater than this value were considered to be responders. In the case of pneumococcal vaccine, this value was 395 arbitrary U/mL; and in the case of Hib, 2.28 μg/mL, as described elsewhere.12,22 To determine a diagnostic criterion of antibody production deficiency, we studied specific antibody response to pneumococcal and Hib conjugate vaccine in the 20 of the 79 healthy adults who received the two vaccines, and the results were compared with those obtained in 22 patients (mean age, 32 years) with humoral immunodeficiencies characterized by defective antibody formation (18 common variable immunodeficiency, 2 immunodeficiency with thymoma, and 2 X-linked agammaglobulinemia).22 Antibody production deficiency was defined as a failure to respond to either vaccine.22 At the beginning of the study sera from the control group and from the bronchiectasis patients were simultaneously obtained. Sera from the patients were stored in aliquots frozen at – 20°C until the assay method to quantify specific antibodies was standardized, normal antibody response to both vaccines established, and antibody production deficiency defined, then they were tested. From then on, all sera obtained from patients were sent immediately for testing.