One of the commonly held concepts regarding allergic fungal sinusitis is that patients with this disorder also demonstrate allergy to other inhalants. However, few published investigations have confirmed this. In this study serum from 16 consecutive patients with histologically proven allergic fungal sinusitis was tested with a seasonal and a perennial radioallergosorbent microscreen disk. The seasonal radioallergosorbent microscreen combines on one disk antigens for two grasses, two weeds, and two trees, and the perennial disk contains Alternaria and dust mite antigens. Total immunoglobulin E was also determined for each sample. Fifteen of the 16 samples demonstrated a radioallergosorbent class II or greater response to both. The total immunoglobulin E level was greater than 100 units/ml in 14 samples (> 1000 in 4 cases) and 97 units/ml in another. This study addresses the presence of inhalant allergy in patients with allergic fungal sinusitis previously described in case reports. The results support the concept that allergic fungal sinusitis is a true allergic (rather than infectious) disease.