The purpose of the present study was to clarify how Barrington's nucleus regulates bladder contractility. Single neurones that discharge at higher rates during micturition contraction were recorded from Barrington's nucleus. Spinal-projecting neurones were identified by antidromic stimulation of the spinal cord. Seventy-six spinal-projecting neurones were classified into four types based on the firing patterns displayed during the relaxation phase of the micturition contraction-relaxation rhythm: (1) ramp-tonic neurones displayed a ramp increase in firing throughout the relaxation phase, (2) ramp-silent neurones were silent initially during the relaxation phase and displayed a ramp increase later, (3) flat-tonic neurones fired constantly, and (4) flat-silent neurones displayed little firing, being virtually silent throughout relaxation. During the relaxation phase, discharge volleys from Barrington's nucleus to sacral neurones were estimated to increase exponentially as micturition contraction approached. Twenty-two neurones increased firing even further within 3 seconds of micturition contraction, suggesting that they are involved in the final stages of initiation of micturition contraction. During micturition contraction, 18 neurones (of which 14 belonged to the ramp-silent class) displayed maximal firing rates before maximal bladder pressures were reached; firing gradually decreased during micturition contraction. Thirty-nine neurones (of which 25 belonged to the ramp-tonic class) displayed constant firing during micturition contraction. This suggests that ramp-silent neurones might be involved in increasing bladder pressure rapidly and strongly via feed-forward regulation, while ramp-tonic neurones might be involved in maintaining high bladder pressure via positive feedback from the bladder afferents. Sixty neurones continued to fire for 1 to 8 seconds after the onset of bladder relaxation, suggesting that Barrington's nucleus does not trigger bladder relaxation.