We report the results of a randomized prospective study comparing a standard bougie rubber balloon dilator [Brown-McHardy (BMH)] and a newer polyethylene dilator passed over a guide wire [Microvasive Rigiflex (MVR)]. Twenty achalasia patients (15M, 5F, mean age 45.4 yr) considered candidates for either dilator were randomized. Symptom assessment, body weight, and upright radionuclide solid esophageal emptying study were measured before and 6 months after pneumatic dilatation. All dilatations were performed by one of three experienced gastroenterologists under fluoroscopic guidance. Overall success occurred with 10/10 BMH and 7/10 MVR. One patient not improved with MVR had myotomy; the other two were successfully treated by BMH. No complications occurred with either dilator.