Evaluation of antral mast cells in nonulcer dyspepsia. Two hundred twenty-five patients with the symptoms of nonulcer dyspepsia underwent clinical and endoscopic evaluation including histologic assessment of endoscopic biopsies. Mast cells were counted after special staining with low pH Alcian blue. Of 225 patients, 31 (13%) were found to have 11 or greater mast cells per high-power field. Endoscopic and routine histologic findings were similar between the subset of 31 patients with 11 or more mast cells and the entire group of 225. The 31 patients with increased antral mast cells had failed treatment with standard drug used for peptic ulcer disease. H1-antagonists improved symptoms in the majority of patients (79%) in whom we had adequate follow-up. Patients with increased mast cells on antral biopsy appear to be subset of patients with nonulcer dyspepsia amenable specific treatment with H1-antagonists. 