Parlo attempted to establish a career in American films but despite a couple of roles in Hollywood films, was unable to extend her European success. In the late 1930s, she was scheduled to appear in the Orson Welles production of Joseph Conrad's Heart of Darkness for RKO Radio Pictures. However, that project did not come to pass. With the outbreak of World War II, Parlo returned to Germany. She appeared in only three films during the last thirty years of her life, making her final film appearance in 1965.