Alfred Hershey and Martha Chase grew some viruses that infect bacteria called bacteriophages on two mediums, one that contained radioactive phosphorous and one that contained radioactive sulfur. Viruses grown in radioactive phosphorous had radioactive DNA and those grown in radioactive sulfur had radioactive protein. When these bacteriophages were allowed to attach to E.coli bacteria, the bacteria that radioactive DNA were radioactive but those that were infected with radioactive protein were not radioactive. This indicated that DNA was passed from the virus to the bacteria. Therefore it was proved by Chase and Hershey that DNA is the genetic material.