We evaluated 148 patients (mean age 45 years) with clinically evident gastroesophageal reflux. A radioisotopic test with 99mTc sulphur-colloid was performed in all; endoscopy in 146, biopsy in 24, acid reflux test and manometric evaluation in 141 and radiologic studies in 85. Sensitivity of the different techniques was: radioisotopes 92%, radiology 87%, acid reflux test 84%; endoscopy 63% and manometric studies 61%. Severity of reflux and esophagitis was adequately predicted from radioisotopic evaluation. We conclude that this radioisotopic test is highly reliable for the diagnosis of gastroesophageal reflux.