This is to communicate the ultrastructural changes of the parietal cells of the human gastric mucosa in “Histalog” stimulation.Gastro-endoscopic biopsy specimens from 48 adult patients suffering from various gastritic conditions are studied. The patients are roughly divided into two groups. The first group consists of the control study. In essentially intact gastric mucosa (hyperacidic) cases, the “Histolog” 50mg had been injected intramuscularly to the subjects and chronologically endoscopic biopsy study had been achieved at 5, 10, 15, 20, 30, and 60 minutes respectively. The second group consists of the study with advanced atrophic gastritis (anacidity) and similar manipulation has been attemped. The obtained specimens were quickly fixed in 2.5% glutaraldehyde, postosmificated, and dehydrated in graded alcohols and embedded in Epon 812. Sections were cut and observed with the Hitachi 11U-B electron microscope with 50kv or 75kv accelerating voltages.