Sacral nerve stimulation (SNS) is effective against faecal incontinence, but the mode of action is obscure. The aim of this study was to describe the effects of SNS on fasting and postprandial rectal motility. Sixteen patients, 14 women age 33-73 (mean 58), with faecal incontinence of various aetiologies were examined. Before and during SNS, rectal cross-sectional area (CSA) and ano-rectal pressures were determined with impedance planimetry and manometry for 1 h during fast and 1 h postprandially. Neither in the fasting state nor postprandially did SNS affect the number of single rectal contractions, total time with cyclic rectal contractions, the number of aborally and orally propagating contractions, the number of anal sampling reflexes or rectal wall tension during contractions. Postprandial changes in rectal tone were significantly reduced during SNS (P < 0.02). Before SNS, median rectal CSA was 2999 mm(2) (range: 1481-3822) during fast and 2697 mm(2) (range: 1227-3310) postprandially (P < 0.01). During SNS, median rectal CSA was 2990 mm(2) (1823-3678) during fast and 2547 mm(2) (1831-3468) postprandially (P = 0.22). SNS for faecal incontinence does not affect phasic rectal motility but it impairs postprandial changes in rectal tone.