Also cast light on Alger Hiss, former State Department official and former Director General of the United Nations. Chambers claimed that Hiss was Communist and had served as a high level spy within the State Department for years. The allegations about Hiss were relayed to the highest level of government, the Oval Office of the White House, where President Franklin Roosevelt was purported to have laughed at the allegation as preposterous. The matter was dropped and Chambers returned to Time magazine where he was promoted to the position of Senior Editor in 1948.

On August 3, 1948, Chambers was called before the House Un-American Activities Committee and reiterated his allegations. He again focused on Alger Hiss. Hiss offered to appear before the committee to deny the charges and was called in on August 5, 1948.

Hiss stated that what Chambers was saying was absolutely untrue and challenged Chambers veracity. Furthermore, Hiss stated that he had never been a Communist and had never even met Chambers. The committee recalled Chambers and told him of Hiss' rebuke. Chambers began revealing specific details about Hiss and his family. His information about the family's personal information was so detailed and so specific, it became apparent that it could only have been obtained through personal knowledge. When Hiss was recalled, he confirmed much of what Chambers had stated about the Hiss family and then acknowledged that he may have known Chambers before, but under his assumed name of George Crosley, when he appearances was different. Chambers later appeared on the Meet the Press television show and reiterated his belief that Hiss was indeed a Communist spy. Hiss sued him for slander.