Hideyuki Kobayashi, male, urologist, completed medical school in 2000 and graduate school in 2006. He was employed as a research associate in the laboratory of Dr. Ralph Brinster, at the University of Pennsylvania, where he had the opportunity to study mouse spermatogonial stem cells. He returned to Japan and, in August 2006, began researching human spermatogonial stem cells, which are difficult to identify and culture in vitro. He is engaged in both general urology and the clinical treatment of male infertility. His research has since progressed from spermatogonial stem cells to pluripotent stem cells. Recently, he has been investigating induced pluripotent stem (iPS) cells derived from patients with male infertility, with the hope of identifying mechanisms and future treatments for male infertility.