The within-examination variation in selected test parameters in repealed pressure-flow studies was determined in a retrospective study of consecutive pressure-flow examinations in 105 patients. It was further evaluated to see whether then was a systematic change in the measured parameters during retesting. To see if variation and reproducibility were influenced by the procedure of investigation, i.e., transurethral or suprapubic, patients were grouped according to the method employed. Finally, the effect of detrusor instability on the measurements was evaluated. Using the Abrams-Griffiths nomogram, patients were classified as obstructed, equivocal, or unobstructed. The test-retest variations in classification were evaluated.