PURPOSE: Internal anal sphincter hypertonia plays a role in the etiology of pain associating fissure in ano (F.I.A), 
thrombosed external haemorrhoids (T.E.H), and in the post operative period for minor anal procedures such as 
hemorrhoidectomy, excision of anal warts or polyps or even after fissurectomy. Nitric oxide is found to be the neurotransmitter that mediates relaxation of IAS in response to recto-anal inhibitory reflex. This report documents a therapeutic role for nitric oxide in the treatment of such painful benign anal conditions. 
METHODS: The study included 230 patients with painful anal conditions. In group (A), including 170 patients with 
chronic anal fissure (76 patients), T.E.H (26 patients), & post-operative (68 patients). Treatment consisted of topical glyceryl tri-nitrate. In group (B), including 60 patients with C.A.F (20 patients), T.E.H (10 Patients) & post-operative (30 patients). 
They received the usual local anaesthetic and antibiotic creams. Manometric studies were performed before, during and after treatment with the evaluation of maximum resting pressure (MRP), maximum squeeze pressure (MSP),& recto-anal 
inhibitory reflex (RAIR). 
RESULTS: In group (A), all patients reported marked relief of anal pain within 3 - 5 minutes following local application 
of glyceryl tri-nitrate cream. Pain relief lasted from three to six hours. Pain control was achieved in 92.11% of patients with C.A.F, 84.61% of patients with T.E.H and 88.23% of patients in postoperative period within 4 days. Healing had occurred in 78.94% of patients with chronic anal fissure, 88.46% of patients with T.E.H & 79.41% of postoperative patients within four weeks of glyceryl tri-nitrate therapy. These results were significantly superior to that obtained in patients in group (B), as pain control was achieved in 70% in patients with anal fissure, 60% in patients with C.A.F & 60% in postoperative patients within 4 days of therapy. Also healing had occurred in 40% of patients with F.I.A, 60% of patients with T.E.H & 70% of patients in the postoperative period within 4 weeks .Manometric studies in patients in group (A) showed significant decrease in MRP , MSP & RAIR values while patients in group(B) showed no significant changes . 
CONCLUSION: Topical application of glyceryl tri-nitrate appears to have a powerful relaxing effect on IAS with a 
significant decrease in MRP and hence help healing and relief of pain associating painful anal conditions.