Summary— In 10 patients with urodynamically proven outflow tract obstruction, detrusor biopsies were taken prior to and following relief of obstruction. The changes in detrusor innervation were compared following the relief of obstruction within the study group and also with an age-matched control group who were urodynamically normal. There was a significant reduction in detrusor innervation in the study group when compared with controls pre-operatively. Within the study group there was a significant increase in detrusor innervation in 8 patients following relief of outflow tract obstruction. Persistence of symptoms after prostatectomy may be explained by failure of detrusor reinnervation.