The within and between examination variation in selected test parameters and test results in repeated pressure-flow studies was determined in a prospective study of consecutive pressure-flow examinations in 22 patients. The patients were pressure-flow tested twice within a month. Furthermore, it was evaluated whether there was a systematic change in the measured parameters during retesting. By using the Abrams-Griffiths nomogram, patients were classified as obstructed, equivocal, or unobstructed. Within and between examination variations in classification were evaluated. We found a systematic Variation in P-det.Qmax during testing, which in the absence of statistically significant systematic variations in P-det.Close and Q(max), indicates a physiological effect of repeated pressure-flow studies, resulting in a less-obstructed second voiding. Supporting this, we found that all patients who changed group of classification of bladder outlet obstruction in the first examination shifted to a group of less obstruction, as did 66% of the patients who changed group of classification of bladder outlet obstruction in the second examination. Still, 80, respectively 85%, of the patients remained in the same group of classification of bladder outlet obstruction during retesting in the first and second examinations, respectively. Classifying the degree of bladder outlet obstruction by Q(max), P-det.Qmax, and P-det.Close 85% of the patients reproduced their test results accurately in both examinations and taking only the first voiding in both examinations into account 95% reproduced their test results. (C) 1999 Wiley-Liss, Inc.