The value and safety of simple needle tap of the abdominal cavity has long been recognized as an aid in the differential diagnosis of the acute abdomen. Despite its value, the procedure has failed to gain general acceptance. This lack of acceptance may be based upon an unjustified fear of puncturing the bowel, or it may be due to the unreliability of former techniques. A survey of the literature combined with our experience in more than 100 cases has served to dispel concern over the rare occurrence of entering the bowel lumen. Diagnostic paracentesis should be considered only as another test to aid in the construction of a more definite, clear-cut clinical picture. This is especially evident in the differential diagnosis of complex or unusual problems associated with intraperitoneal disease or traumatic injury. In many instances the results of a tap are conclusively self-explanatory and the clinical problem is at