Investigation of mode of action of biofeedback in treatment of fecal incontinence. A study was carried out in 25 incontinent patients to evaluate some of the factors thought to be responsible for the success of retraining for fecal incontinence. Subjects were initially allocated to one of two groups; one group was trained to perceive small rectal volumes (active retraining), the other group carried out the same maneuvers but were not given any information or instruction. Active sensory retraining reduced the sensory threshold from 32 +/- 8 to 7 +/- 2 ml (P less than 0.001), corrected any sensory delay that was present (P less than 0.004), and reduced the frequency of incontinence from 5 +/- 1 to 1 +/- 1 episodes per week (P less than 0.01). Sham retraining caused a modest reduction in the sensory threshold (from 29 +/- 9 to 20 +/- 8; P less than 0.05) but did not significantly reduce the frequency of incontinence. Subsequent strength and coordination training did not significantly improve continence, although at the end of the study, 50% of patients had no incontinent episodes at all and 76% of patients had reduced the frequency of incontinence episodes by more than 75%. This improvement in continence was not associated with any change in sphincter pressures or in the continence to rectally infused saline but was associated with significant improvements in rectal sensation. The functional improvement was sustained over a period of two years in 16 of the 22 patients available for follow-up. In conclusion, the results support the use of retraining in the management of fecal incontinence and suggest that retraining may work by enhancing rectal sensitivity and instilling confidence. 