Bronchiectasis occurs in patients with immunodeficiency and fungal hypersensitivity disorders. To assess the prevalence of abnormal humoral immune parameters in bronchiectasis, a retrospective study was carried out on sera from 30 patients. Studies included immunoglobulin quantitation and specific antibody to fungal species. Eleven patients were found to have immunodeficiency (nine with panhypoglobulinemia and two with selective IgM deficiency). Six patients had elevations of serum IgA and four patients had elevations of serum IgE. Six patients had elevated total antibody to Aspergillus or Candida species and six had precipitin bands to one or more fungal antigens. This study indicates that immunodeficiency is prevalent and plays a causative role in some patients with bronchiectasis. Hypersensitivity reactions to Aspergillus, Candida, and other ubiquitous environmental fungi may also play an etiopathogenic role in this disease (bronchiectasis, humoral immunity, immunodeficiency).