Twenty-five (18%) of 140 incontinent patients and 6 (17%) of 35 normal controls showed episodes of spontaneous internal sphincter relaxation during 30 min multiport manometric and electromyographic recording under resting conditions. The episodes lasted at least 15 s and reduced the pressure in the outermost anal channels by at least 20 cm of water. Patients exhibited more episodes of relaxation than controls (4.3 +/- 0.6 vs 2.3 +/- 0.2 per subject; mean +/- SEM; p less than 0.05) and the pressures fell to lower values (19 +/- 1 vs 42 +/- 5 cm water, p less than 0.01), but the duration of relaxation was not significantly different (53 +/- 4 vs 40 +/- 7 s). Episodes of spontaneous relaxation were associated with simultaneous rectal contractions in 33% of the normal subjects and 45% of incontinent patients. Unlike normal subjects, most of the episodes of transient relaxation recorded in the incontinent group were not associated with compensatory increases in the electrical activity of the external anal sphincter (77% vs 17%; p less than 0.05). Over 50% of the incontinent patients who showed spontaneous relaxation also showed post squeeze or post-strain IAS relaxations whereas these were seen in less than 6% of the normal subjects with spontaneous relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)