We examined pressure-flow test results in 28 male patients with micturition disturbance in whom it is difficult to determine whether bladder outlet obstruction or impaired detrusor contractility is the cause. One reason that some patients do not improve after prostatectomy is that detrusor contractility was not estimated before preoperatively. The degree of infravesical obstruction and of detrusor function were assessed by the method of Griffiths' diagram (maximum flow rate versus corresponding detrusor pressure). Three patients showed infravesical obstruction, 11 equivocal obstruction, and 14 no obstruction. No patients showed strong detrusor function, 14 normal function, and 14 weak function. Eleven patients underwent TU-procedure. Two patients with normal detrusor function and infravesical obstruction showed good postoperative improvement of uroflowmetry results, but 4 patients with weak detrusor function and no infravesical obstruction showed no improvement. Preoperative assessment of the degree of infravesical obstruction and of detrusor function by pressure-flow testing is therefore considered useful. We emphasize that preoperative evaluation of detrusor function is an important aspect of treatment of male micturition disturbance.