The following protocol describes the isolation of radioactive viral and subviral particles from infected cells. This protocol has been written for isolation of poliovirus particles from H1 HeLa cells. Infection protocol and timing of [³⁵S] methionine labeling and particle collection should be tailored to the virus of interest. Following isolation of the viral particles, the viral proteins present in these particles may be separated by gel electrophoresis and visualized by autoradiography.