The principles and technic of the double contrast examination of the esophagus, stomach, and duodenum are outlined. Use of the hypotonic agent glucagon improves evaluation of the stomach, but optimal visualization of the duodenum may require reexamination after its effect has worn off. The technic is able to show gastric erosions and linear ulcers, both of which are rarely recognizable with conventional examination. The characteristics of malignant gastric ulcers and the presence of fundal lesions are also better demonstrated on double contrast evaluation. Small esophageal carcinomas may be recognized on a double contrast barium swallow. Examples of each of these lesions are illustrated. Many ulcerating lesions are seen “en face” on double contrast, and not in profile, which may require relearning the interpretation of their appearances. For greatest accuracy the double contrast technic should be combined with the conventional examination. As this therefore becomes a more time-consuming examination, we advocate its use only in selected clinical situations rather than on a routine basis.