The artificial introduction of air into the peritoneal cavity as an important part of the medical management of tuberculosis is widely known. The use of this procedure as a vital diagnostic tool, however, is less familiar. We are convinced that it is unexcelled for the diagnosis of upper intra-abdominal masses outside of the stomach and intestines, especially if it is combined with a contrast study of the gastrointestinal tract. The procedure is simple and innocuous and devoid of any unpleasant sequelae, since the amount of air introduced is much less than is ordinarily employed in therapeutic artificial pneumoperitoneum. It is thus handy and convenient, as it can easily be performed on an outpatient basis. Our technic consists simply in the introduction of a 22-gauge needle by a right or left para-umbilical route, the same needle being used for local anesthesia and for penetrating the peritoneal cavity. If the patient is obese, a 22-gauge spinal needle is used following local anesthesia. To determine the...