Immunologic defects in patients with refractory sinusitis. Sixty-one patients with chronic sinusitis who were referred for an allergy evaluation were evaluated for immunologic competence including assessment of quantitative serum immunoglobulin levels, IgG subclass levels, and response to pneumococcal and Haemophilus influenzae vaccines. In addition to chronic sinus disease, recurrent otitis media and asthma exacerbation were common problems in this group. Five patients had an elevated age-adjusted IgE level and 22 patients had positive prick tests to one or more environmental inhalants; these findings suggest an allergic component in this subgroup. Twelve additional patients had highly reactive intradermal tests to common environmental allergens, which also may be clinically significant for underlying atopy. Eleven patients had low immunoglobulin levels, 6 had low immunoglobulin levels and vaccine hyporesponsiveness, and 17 had poor vaccine response only. Thus, 34 of 61 patients with refractory sinusitis had abnormal results on immune studies, with depressed IgG3 levels and poor response to pneumococcal antigen 7 being most common. In addition to allergy, immunologic incompetence may be an important etiologic factor in patients with chronic, refractory sinusitis. 