The mucin profile of 24 endoscopic biopsies of heterotopic gastric mucosa (HGM) of the upper esophagus in adults and a control group of ten cases of Meckel's diverticula containing heterotopic gastric mucosa were studied with two combined histochemical methods: alcian blue pH 2.5/PAS and high iron diamine/alcian blue pH 2.5. The clinical and light microscopic features of the 24 HGM cases were also reviewed. In addition to overall secretion of neutral mucins by the 24 HGM cases, mucin histochemistry showed prominent secretion of acidic mucins in 19 of 24 HGM cases (79%), with sulphomucins in 11 of 24 HGM cases (45.8%). This mucin profile of HGM was unlike that of either normal gastric mucosa or heterotopic gastric mucosa in Meckel's diverticula. Moreover, a comparison between the mucin profile and clinical features of HGM and Barrett's esophagus showed certain similarities. The data suggest a physiopathologic link between HGM and Barrett's esophagus.