Provided are methods for sterilizing a material comprising a biologically-active agent comprising irradiating said material with ionizing radiation at a dose of about 5 kGy to about 25 kGy while maintaining said material in an atmosphere comprising at least 95% by volume inert gas and at a temperature of about 4° C. or lower. Also provided are sterilized materials comprising a biologically-active agent, wherein said materials exhibit substantially the same amount of biological activity as a non-sterilized control.