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The working title of this film was Three Were Thoroughbreds. Kenneth Perkins' novel was first published in Blue Book magazine in June 1938. Relentless was the initial effort of Cavalier Productions. According to a Columbia publicity item in the file on the film at the AMPAS Library, exteriors for this picture were shot around Tuscon, Arizona. On June 7, 1948, Lux Radio Theatre presented a radio broadcast of the story, starring Robert Young and Claire Trevor.