We compared the measurements obtained with different systems presently used to study the pressure characteristics of the anal channel (an open perfusion probe, a closed perfusion probe and a microtransducer). We also studied rectal sensitivity to distention in an attempt to define the exactness and reliability of the measurements made with these different techniques. The results indicate that although the measurements obtained vary with the diameter of the catheters used, the differences were not statistically significant. In contrast, the maximum tolerated volume of patients is greater with a slow and continuous rhythm of infusion than when saline is infused rapidly and in boluses. The published literature is reviewed and results are discussed, as well as the advantages and disadvantages of different methods.