Nine previously unreported rectal injuries caused by bariumenema examinations have been reviewed. In each case, the injury occurred in conjunction with inflation of a rectal balloon. Analysis of the clinical material suggested that certain mechanical properties of balloon catheter tips might transfer mechanical stress to the rectal wall and contribute to the observed injuries. Careful manometric evaluation of in vivo rectal balloons suggest that significant anatomic differences in patients may be clinically important. Further experimental bench studies revealed undesirable mechanical properties in many commercially available rectal balloon catheters. These mechanical problems include low compliance, asymmetrical inflation, strong lateral and anterior displacement of a firm catheter tip into the restraining wall, and self-obstruction of the balloon deflation outlet by the inflated balloon. Many of these problems were clinically confirmed by careful in vivo observations and by evidence collected from the nine cases of rectal injury. A series of practical prophylactic procedures are recommended.