A research team reports a novel function of fibroblast growth factor 2 (FGF2), a self-renewal factor for spermatogonial stem cell (SSC) which is the origin of sperm production. Although it has demonstrated that both FGF2 and glial cell line-derived neurotrophic factor (GDNF) is indispensable for SSC self-renewal and survival in vitro, the present study reveals that FGF2 has different properties from GDNF in mouse testis. This finding will contribute to the regulation of SSCs in vivo for the treatment of male infertility.