Tc-99m-Pertechnetate (TcO4) is concentrated by the stomach after intravenous injection, allowing the detection of ectopic gastric mucosa. It has been used to develop a noninvasive test of gastric secretion. However the cellular site of concentration is still controversial, that is whether mucin-secreting epithelial cell or acid-secreting parietal cell. This study is planned to investigate the effects of cimetidine and gastric acidity on the retention of TcO4 in the gastric wall of the rat. Also we further attempted to clarify the uptake and secreting cell of TcO4 in the gastric mucosa. One hundred rats were divided into two groups, preliminary (40 rats) and main examination group (60 rats). Preliminary examination group was composed of fasting group (20 rats) for the detection of the time for reaching stable TcO4 retention ratio in gastric wall and post-prandial group (20 rats) for the detection of the time for reaching the maximal gastric acidity. Main examination group was composed of fasting group (30 rats), which was subdivided into control group (10 rats), cimetidine group (10 rats), Mylantaⓡ group (10 rats) and post- prandial group (30 rats), which was subaivided into 90 min group (10 rats), 90 min cimetidine group (10 rats), and 120 min group (10 rats). Retention ratio (%) of TcO4 in the gastric wall and the pH of the gastric contents were measured in the extracted stomach of the six groups. Gastric wail retention ratio of TcO4 was calculated by the gastric wall radioactivity (cpm) divided by total gastric radioactivity (cpm) at 30 mins after intravenous injection of 0.4 mCi of TcO4. The results were as follows: 1) The time required for reaching stable TcO4 retention ratio and the lowest gastric PH were 30 min and 90 min, respectively. 2) In the fasting group, the gastric wall retention ratio of TcO4 was significantly increased in the cimetidine group, compared with the control group (P〈0.01). However there was no significant difference between the control and Mylantaⓡ group. 3) The TcO4 retention ratio and gastric pH were well correlated in the post- prandial 120 min group (r=0.7112, p〈0.05), in the post-prandial 90 min and 90 min cimetidine groups correlated poorly. However, there was no correlation in the three fasting groups at all. Referring the above results, we infer that TcO4 is secreted into the gastric lumen by both parietal and non-parietal cells, with dominant non-parietal TcO4 secretion in the fasting state and dominant parietal TcO4 secretion in the stimulated state.