['Although invasive pneumococcal disease is infrequent in cystic fibrosis (CF), it is recommended that all patients with CF receive pneumococcal immunization. As part of a comprehensive program to immunize our clinic population, we obtained preimmunization anti-pneumococcal antibody levels. We hypothesized that the percentage of CF patients without protective levels of anti-pneumococcal antibody levels would be high, as they are exposed to frequent antibiotic therapy that may eradicate organisms before generation of an antibody response.', 'An observational study of 100 patients with CF, aged 1 to 39 years, was conducted in a regional CF center. Preimmunization anti-pneumococcal antibody levels against 6 serotypes were measured by enzyme-linked immunosorbent assay. Protective antibody levels were defined as >200 ng/mL.', 'A majority of CF patients-61% to 100%, depending on age and serotype-had protective levels of pneumococcal antibody. There was a significant positive correlation between antibody level and age for 5 of the 6 serotypes tested.'] Are preimmunization anti-pneumococcal antibody levels protective in a majority of patients with cystic fibrosis?