Elevated total serum IgE is helpful in making the diagnosis of ABPA and in monitoring the onset of exacerbations and response to therapy. ABPA occurs frequently in patients with CF, and in these instances a high total serum IgE is seen. This is the first case report of ABPA without an elevated total serum IgE level. At no time prior to this patient's first episode of ABPA, at the time of the illness, or at monthly intervals during follow-up did her total serum IgE level exceed 29 IU/ml.