A technique is demonstrated to evaluate the functional relevance of the sacral spinal nerves regarding anal sphincter function. Sacral spinal nerves S2, S3, S4 can be reached selectively for electrical stimulation by a dorsal approach through the sacral foramina. Electrical stimulation of S3 and S4 results in visible contraction of the different striated muscular anal sphincter components and in an increase of anal canal closure pressure. These effects differ among individuals. Thus, the functional relevance of each single sacral spinal nerve on the striated muscular anal sphincter can be tested specifically.