This study was designed to compare the effect of topical glyceryl trinitrate (GTN) and oral nifedipine treatments on maximal anal resting pressure (MARP) and subsequently to assess their effectiveness in healing of chronic anal fissure (CAF). Patients were allocated randomly to receive either oral nifedipine retard (10 patients) 20 mg twice daily or instructed to apply glyceryl trinitrate (0.2 percent) ointment (10 patients) into the lower half of the anal canal twice daily. They were reviewed and assessed at the first visit and every fortnight for measurement of MARP, pain scores, blood pressure, pulse rate, healing of the fissure and adverse effects. Treatment were continued until healing had occurred or for up to 8 weeks. MARP values before and after application of the GTN ointment was 113.2 cm H2O and 72.5 cm H2O respectively (P < 0.001). Nifedipine caused a reduction in mean MARP from 105.2 to 74.0 cm H,0 (P < 0.001). Linear analogue pain scores were significantly reduced after 2 weeks treatment with GTN and nifedipine (P < 0.001) and continued throughout the treatment period. At the end of the study; 7 of the 10 patients in the GTN group were deemed to be healed (5) or improved (2), compared with 6 of the 10 patients in the nifedipine group (5 healed, 1. improved). Headaches occurred in 3 patients in the GTN group, compared with one patient in the nifedipine group. There was no significant difference between GTN and nifedipine in terms of reduction in MARP and pain score, healing of the fissure and incidence of early recurrence and side effects of treatments. We conclude that GTN ointment and oral nifedipine are equally effective in the treatment of chronic anal fissure.