Internal anal sphincter manometric and myoelectrical investigations were performed under basal conditions and in response to rectal distension in 17 patients with chronic anal fissures and 15 controls. Measurement of sphincter pressures were carried out by pull-through technique, using water perfused open-tip-catheters. Electrical signals were obtained employing concentric needle electrodes inserted into the internal anal sphincter. No statistically different resting pressures were noted between patients with fissures and controls. Just so no significant difference were found in frequency and amplitude of slow potentials generated by the internal and sphincter. Neither amplitude or frequency correlate with anal sphincter pressures. In both groups, transient rectal distension produced relaxation of the internal sphincter and were associated with inhibition or irregularity of electric activity. Distribution and amplitude of internal overshoot contraction showed no difference in both groups. It can be concluded that internal sphincter spasm can not be considered as the sole cause for persistence of fissures.