Upper respiratory symptoms and sinusitis constitute a major reason for patient visits to their physician. The diagnosis of sinusitis is often made based on history and physical exam, but the accuracy of such diagnosis is questioned. Sinus films or CT scans are expensive. Obtaining pus from the middle meatus is impractical. We studied whether analysis of four easily measured substances (protein, pH, leukocyte esterase and nitrite) in nasal secretions could predict the presence or absence of bacterial sinusitis, as diagnosed by history combined with sinus x ray or CT. We enrolled 217 consecutive patients, aged 4-61 years, with clinically suspected bacterial sinusitis (duration of symptoms, 7-26 days), who had radiographic studies. All had their nasal secretions assayed using a simple rapid test. A clinical scoring system was developed to allow for a simple interpretation of test results of four assays in a single clinical score. All 52 patients with scores of 0 or 1 were CT or x-ray negative for bacterial sinusitis. All 144 with scores of > or =4 were imaging study positive. Of the 21 patients (10%) with scores of 2 or 3, 14 were imaging study negative and 7 were positive. We concluded that combining these four separate assays on nasal secretion into one number, it is possible to rule in or rule out bacterial sinusitis in 90% of patients. This inexpensive, simple test can decrease the cost and help increase the accuracy of the diagnosis, thus improving the care of patients with bacterial sinusitis.