Fifteen of twenty patients with the solitary rectal ulcer syndrome, eighteen of whom were women, had evidence of reinnervation in the external anal sphincter muscle as demonstrated by single fibre EMG and nine of these patients had an increased pudendal nerve terminal motor latency. In ten patients there was paradoxical puborectalis muscle activity on straining, but damage to the innervation of the external anal sphincter muscle was correlated with a history of straining, and with excessive perineal descent, rather than with paradoxical puborectalis activity. We suggest that this syndrome does not have a single cause.