Thirteen patients with nonseminomatous testicular germ cell tumours underwent nerve-sparing retroperitoneal lymphadenectomy (RLA) with prospective isolation and preservation of postganglionic sympathetic nerve fibres. In all ten patients with pathological stage I in whom a unilateral nerve-sparing RLA was performed, ejaculation was preserved. In two of three patients with pathological stage IIa who underwent a bilateral RLA with a nerve-sparing technique on one side, ejaculation was also preserved. In nine patients intraoperative electrostimulation of isolated sympathetic nerve fibres was performed employing Brindley's stimulation device. The result was an immediate and reproducible ejaculation in seven patients. Thus electrostimulation of sympathetic nerves may be a useful intraoperative test for the identification of the nerve fibres that need to be protected for ejaculation. Nerve-sparing RLA seems to be superior to modified (unilateral) RLA with regard to preservation of ejaculation.