The effect of cimetidine, an H2-receptor blocking agent, on the secretion of 99mTc-pertechnetate was studied in 11 dogs. In cimetidine-treated animals, there was increased retention of 99mTc-pertechnetate by the gastric wall as compared with the untreated animals. The results indicate the potential use of cimetidine for enhanced visualization of Meckel's diverticulum, Barrett's esophagus, and the stomach, with 99mTc-pertechnetate.