Utilizes an innovative technique: scenes spoken in Russian begin in Russian and after a couple of interchanges segue to being spoken in English, avoiding either usual extreme of subtitling or dubbing into English. Was first used in movie Judgment at Nuremberg in 1961.
John Huston said of this film in his auto-biography 'An Open Book': "I thought 'The Kremlin Letter' had all the makings of a success... The book by Noel Behn had been a best-seller. It had, moreover, all those qualities that were just coming into fashion in 1970 - violence, lurid sex, drugs. The cast was exceptionally strong... and the performances couldn't have been bettered. It was extremely well photographed [by Edward Scaife] - there was a virtuosity, a shine to it. Gladys Hill and I wrote the script, which I considered quite good, though in retrospect it was perhaps overcomplicated."
This picture was filmed in four countries: Finland, Italy, Mexico, and the USA. The scenes set in Moscow were shot in Helsinki, Finland.
Initially, Steve McQueen was offered the part of Charles Rone, but turned it down. John Huston also considered Warren Beatty and Robert Redford for the part before signing Patrick O'Neal, whom he had strongly considered as a replacement for Montgomery Clift in his earlier film, Reflections in a Golden Eye (1967) prior to his hiring Marlon Brando instead.
Source novelist Noel Behn based his novel of 'the Kremlin letter' on his experiences in working for the US Army's Counterintelligence Corps.