Multiport anorectal manometry and external anal sphincter (EAS) and internal anal sphincter (IAS) electromyography were conducted in 15 males (41 +/- 3 years) and 20 females (43 +/- 2 years; 5 nulliparous) during rest, maximum conscious sphincter contraction, rectal distension and increases in intra-abdominal pressure. The basal pressure declined within 15 minutes of insertion of the manometric probe to a stable plateau, 55 +/- 4% of the initial value. The maximum basal (91 +/- 5 vs 61 +/- 6 cm water; mean +/- SEM), minimum basal (43 +/- 7 vs 27 +/- 3 cm water) and the maximum squeeze pressures (257 +/- 20 vs 107 +/- 13 cm water) were higher (p less than 0.05) in males than females. Distension of a rectal balloon caused a reduction in pressure in all anal channels, that increased in depth and duration as the distending volume was increased. These anal relaxations were associated with rectal contractions and transient increases in the electrical activity of the EAS. Upon deflating the balloon, the anal pressure increased to values that exceeded the pre-inflation values. The pre-inflation (89 +/- 4 vs 49 +/- 4 cm water), post-inflation (104 +/- 9 vs 62 +/- 7 cm water) and residual (47 +/- 4 vs 30 +/- 2 cm water) pressures during rectal distension were significantly higher in males than in females (p less than 0.05). The higher residual pressure in males was associated with a higher EAS index during rectal distension (0.94 +/- 0.10 vs 0.65 +/- 0.10 mv s; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)