PURPOSE:This study was designed to investigate rectal reservoir function and anal pressures in patients with fecal incontinence using anorectal manovolumetry and to evaluate the reproducibility of the investigation.METHODS:Forty‐eight patients with fecal incontinence were investigated with respect to anal pressures and rectal volume changes and sensibility in response to stepwise increased rectal pressures (5‐60 cm of H2O). Patients with known rectal wall diseases were excluded. Results were compared with those of 25 control subjects investigated in a similar manner. In ten individuals in the latter group, investigation was repeated after 5 minutes and 24 hours.RESULTS:Resting pressure (RP), squeezing pressure (SP), and the difference between SP and RP was lower in patients than in controls(P<0.0001). There was no significant difference between patients and controls concerning rectal sensibility or compliance(P>0.05), but there was a correlation between RP and rectal compliance(r=0.25;P<0.05) and between SP and rectal compliance(r=0.30;P<0.01). There was good reproducibility of RP and SP after five minutes(r=0.88‐0.92;P<0.001). The day‐to‐day variation was larger for RP(r=0.52;P>0.05) compared with SP(r=0.89;P<0.001). Rectal compliance at 40 cm of H2O was reproducible after 5 minutes(r=0.98;P<0.0001) and 24 hours(r=0.88;P<0.01).CONCLUSIONS:These results indicate that the primary defect in incontinent patients is a sphincter dysfunction. Any reduction in rectal compliance is likely to be a secondary phenomenon.