Ouch...

news @ nature.com - Stem cells found in adult mouse testes -Procedure could yield an ethically sound source of stem cells.

From the above story in Nature:

Researchers in Germany have identified a potential source of reprogrammable cells in adults that could be used for regenerative therapy. The cells would be taken directly from the testis and cultured....

....it should be possible to produce similar results [to those with mice] with samples taken from human testicles through a biopsy...