From the November 9-15, 1963 edition of TV Guide, Minneapolis-St. Paul edition: Would you believe the 1954 sci-fi/horror movie about giant mutant ants called "Them!" was shown on Masterpiece Theatre? How did the highly cultured Alistair Cooke introduce that one?
In all fairness, this Masterpiece Theatre was not the long-running PBS show produced by WGBH Boston that primarily featured British drama and premiered in 1971, but was simply the name given by then-ABC affiliate KMSP-TV Channel 9 to their late night movie.
While most probably wouldn't consider "Them!" to be a masterpiece, critic and movie guide author Leonard Maltin gives the thriller three and a half (out of four) stars, praising it for an "intelligent script" and being "extremely well directed." This particular masterpiece featured James Whitmore, Edmund Gwenn, a pre-Gunsmoke James Arness and a pre-Davy Crockett Fess Parker.