Sacral nerve stimulation (SNS) has an established role in treatment of faecal incontinence, however the mechanism of action remains unknown. Our laboratory has previously shown that acute SNS augments somatosensory cortical potentials evoked by anal canal stimulation in a rat model (Griffin et al., 2011). The aim of this study is to examine the effect of acute SNS on motor function of the anal sphincters in the same animal model. Eight virgin female Wistar rats were anaesthetised with urethane (1.5g.kg-1 i.p.). The combined force of the internal anal sphincter (IAS) and external anal sphincter (EAS) was measured using a force transducer, by mounting the distal 4-5mm of the anal canal as an isometric ring preparation in situ. A novel method was used to separate the EAS and IAS force recordings by stimulating the inferior rectal nerve (which supplies the EAS) at 1Hz. The frequency and amplitude of the slow waves of the IAS were also measured. Three minute recordings were taken before, during and after SNS at S1 [1ms pulses at 10Hz and at 0.5-1.1 Volts (just above motor threshold)]. A balloon was then inserted into the rectum and inflated with 0.3ml saline for 10 sec to evoke the recto-anal inhibitory (RAIR) and recto-anal excitatory (RAER) reflexes. Cortical evoked potentials were recorded in 8 rats as described previously. The results were analysed with repeated measures ANOVA. The criterion for statistical significance was p<0.05. SNS did not have any significant effect on the IAS force (p=0.135), EAS force (p=0.126), slow wave frequency (p=0.239), slow wave amplitude (p=0.999), RAIR (p=0.202) or RAER (p=0.268). However the amplitude of cortical evoked potentials increased by a mean of 62% (SEM=16) after SNS. The experiment suggests that SNS does not have a direct motor effect. From our current and previous study of anal canal cortical evoked potentials, it appears that the mechanism of action is through augmentation of sensory feedback to the cortex. These results reflect the clinical use of SNS as the current is delivered at the sensory (sub-motor) threshold.