Eleven patients with idiopathic faecal incontinence (IFI) and nine normal controls were studied with techniques of mucosal electrosensitivity and rectal distention for the quantitative assessment of anal and rectal sensation and with manometric and electromyographic tests for the assessment of anorectal motor function. The tests of motor function showed pelvic floor motor neuropathy in the patients with IFI, compared with controls, anal canal resting and voluntary contraction pressures were significantly (p less than 0.05, p less than 0.002) lower, pudendal nerve terminal motor latency and external anal sphincter fibre density were significantly (p less than 0.05, p less than 0.05) raised. The results of mucosal electrosensitivity (MES) disclosed a sensory deficit in the anal canal in patients with IFI, compared with controls, MES threshold was significantly (p less than 0.002) higher. Sensory thresholds to rectal distension were similar in the two groups. This study shows that sensory deficit of the anal canal occurs in combination with the motor neuropathy of the anal canal musculature in primary neuropathic faecal incontinence.