An intraoperative test to identify emission relevant lumbar postganglionic nerves during nerve sparing retroperitoneal lymph node dissection is presented. The neurophysiological course of the ejaculation into the posterior urethra, the emission, is described. A retroperitoneal nerve sparing procedure was done for nonseminomatous testicular tumors bilaterally in 7 patients with pathological stage I disease and unilaterally in 4 with pathological stage IIa disease. While the isolated lumbar nerves were electrostimulated, the seminal vesicles and bladder neck were monitored by suprapubic transvesical sonography. Simultaneously, endoscopy of the posterior urethra was performed and time code was registered. Emission began with bladder neck closure, propulsive contraction of the seminal vesicles in the periphery and opening of the paracollicular region. Then, complete contraction of the seminal vesicles was associated with closure of the prostatic urethra and ended in the separate secretion from the ductuli prostatici and ejaculatorii. Descending from nerve L1 to L3, their importance for emission usually increased. For intraoperative monitoring of emission transvesical sonography alone is sufficient. In 2 patients this method allowed us to identify the relevant nerves within the retroperitoneal residual mass (fibrosis) after chemotherapy.