Abstract: Disclosed herein are methods of inactivating viruses that may be present in human platelet lysate (hPL) by exposure to ionizing radiation. Surprisingly, the hPL retains an acceptable amount of bioactivity without requiring freeze-drying or the addition of a stabilizer. The hPL can be used as a supplement for in vitro culture of various cell types, especially human mesenchymal stromal cells (hMSCs) and for various therapeutic applications.