The results of transvesical phenol injection into the paravesical nerve plexuses are reported in 40 consecutive patients. A 58% success rate was achieved in the treatment of refractory detrusor instability and 73% success was seen in detrusor hyper-reflexia in 11 patients with multiple sclerosis. Urinary retention occurred in 8%. Troublesome complications were seen in 2 patients who had had previous pelvic radiotherapy, which should be regarded as an absolute contraindication to the procedure.