The contribution of the resting anal canal pressure (RAP) and the maximal squeeze pressure (MSP) to the problem of fecal incontinence was assessed by comparing 143 incontinent patients to a control population of 157 healthy subjects. These parameters were determined using a multilumen continuously perfused catheter and a mechanized rapid pull-through technique. In 10 male volunteers both RAP and MSP were determined using catheters that varied from 3 mm to 18 mm in diameter. In the control population, the RAP was significantly lower in females 40 years of age and over as compared to males. MSP values were significantly lower in females at virtually all ages. In women, parity did not correlate with RAP (coefficient = -0.099, P greater than 0.05) and MSP (coefficient = -0.123, P greater than 0.05) and any decrease in pressures was related to aging. Aging in women was associated with a consistent reduction in RAP (coefficient = -0.614, P less than 0.00005) and MSP (coefficient = -0.372, P = 0.0006). In males, there was a similar but less impressive age-related reduction for the RAP (coefficient = -0.333, P = 0.006) but not for the MSP (coefficient = -0.196, P greater than 0.05). Nine percent of the volunteer population were essentially unable to increase the RAP with maximal squeeze efforts. A linear increase in anal pressures was recorded as catheter diameter increased from 3 to 12 mm. Normative data for the RAP and MSP (mean +/- 2 SD) were constructed for each sex on a decade basis and showed a wide range of pressures for each age grouping. In the group with fecal incontinence (FI) 39% of females and 44% of males fell within the "normal" range for both the RAP and MSP. For all patients with FI, 41% and 17% had impairment of one or both parameters, respectively. It is concluded that: aging affects the RAP in both sexes but to a greater degree in women. The MSP is related to aging in women only; child bearing has no effect upon these parameters; clinical problems of bowel control can occur when sphincter pressure measurements are within the low "normal" range; and recording instrument diameter consistently affects RAP and MSP.