We have studied 30 patients with idiopathic (neurogenic) faecal incontinence using anorectal manometry and concentric needle and single fibre electromyographic methods. We have measured the terminal motor latency in the pudendal nerves of these patients using a new digitally directed transrectal stimulation and recording technique (right mean (+/- s.d.) 3.2 +/- 0.9 ms, left mean (+/- s.d.) 3.0 +/- 0.9 ms) and compared the results with those obtained from 28 normal subjects (right mean (+/- s.d.) 2.0 +/- 0.5 ms, left mean (+/- s.d.) 1.9 +/- 0.3 ms). These differences between normal and incontinent patients were significant (P = 0.01) using the Wilcoxon Rank Sum Test. The findings support the hypothesis that idiopathic (neurogenic) faecal incontinence is due to damage to the nerve supply of the pelvic floor musculature.