Factors which predispose some men with benign prostatic hyperplasia to chronic urinary retention whilst others develop acute retention are not understood. In order to assess whether there is an occult neuropathy associated with chronic retention, neurophysiological measurements were used to test the integrity of the lower urinary tract nerve supply. A series of 22 male patients with chronic urinary retention secondary to prostatic hyperplasia underwent sacral reflex latency measurement; 73% demonstrated a sensory suprasacral abnormality with intact spinal reflex arcs. These results suggest that although the sacral reflex pathways are intact, there is a sensory/proprioceptive abnormality in the higher neurological centres which may be an adaptive mechanism to the presence of bladder outflow obstruction.