Forty-seven biopsies of gastric mucosa and Barrett esophagus from 32 patients were studied with the argyrophilic nucleolar organizer region method. Twenty-two biopsies were gastric and 25 esophageal. Four showed normal noninflamed mucosa, 14 reactive glandular changes, eight intestinal metaplasia without dysplasia, ten low grade dysplasia with intestinal metaplasia, and 11 high grade dysplasia. The mean number of nucleolar organizer regions was 14.9 for high grade dysplasia, 10.9 for low grade dysplasia, 8.5 for intestinal metaplasia without dysplasia, 6.7 for reactive changes, and 3.9 for normal mucosa. The difference between high grade dysplasia and the other groups was significant (P = 0.004). However, the difference between high and low grade dysplasia was not significant (P = 0.06), and there was an overlap between reactive and high grade dysplastic lesions. We conclude that although nucleolar organizer counts correlate with the degree of dysplasia, the technique is of limited practical use.