Background. The purpose of this study was to demonstrate the effect of oral nifedipine on maximal resting anal pressure (MRAP) in healthy volunteers and to evaluate its role in the treatment of chronic anal fissure (CAF). Methods: MRAP was measured in 10 healthy volunteers and 10 patients with CAF before and after oral nifedipine (20 mg b.i.d.). Patients were assessed on the first visit and every fortnight for measurement of MRAP, pain scores, blood pressure, pulse rate, healing of the fissure and adverse effects. Treatments were continued until healing had occurred or for up to 8 weeks.. Results: MRAP values before and after nifedipine were 73.2 and 49.3 cm H2O, respectively, in healthy volunteers (p < 0.001). Nifedipine caused a reduction in mean MRAP from 105.2 to 74.0 cm H2O (p < 0.001) in patients with CAF. Pain scores were significantly reduced after 2 weeks of treatment with nifedipine (p < 0.001) and continued throughout the treatment period. At the end ofthe study 6 of the 10 patients treated with nifedipine were deemed to be healed (n = 5) or improved (n = 1). Headache occurred in 1 patient. Conclusion: We conclude that oral nifedipine is effective in reducing MRAP and should become the first-line treatment for CAF. Copyright (C) 2003 S. Karger AG, Basel.