OBJECTIVE To describe positional variation in the outcome of the Whitaker test. METHODS The authors retrospectively reviewed the cases of six patients in whom the pressure gradient during Whitaker testing varied by at least 10 cm of water and changed from normal ( < or = 13 cm of water) to abnormal ( > 13 cm of water) when patients were placed in different positions. RESULTS Four patients had obstruction only in nonstandard positions. All had intermittent symptoms, and three had ureteral kinks at fluoroscopy. Two patients with ileal conduits had abnormal results in the standard position but normal results at repositioning related to compression of the conduits (seen as conduit distention at fluoroscopy). All six had undergone urinary tract surgery. Gradient differences with positional change ranged from 10 to > 38 cm of water. CONCLUSIONS Whitaker testing in different positions may help identify intermittent obstructions that might otherwise go undetected or prevent inappropriate diagnosis of obstruction. Intermittent or unexplained symptoms, tortuous ureters, malpositioned kidneys, or previous surgery are indications for provocative positional testing.