In 1956, nine years before being cast as Dr. McCoy, Kelley played a small supporting role as a medic in "The Man in the Gray Flannel Suit" in which he utters the diagnosis "This man's dead, Captain" and "That man is dead" to Gregory Peck. Kelley appeared as Lieutenant Commander James Dempsey in two episodes of the syndicated military drama "The Silent Service", based on actual stories of the submarine service of the United States Navy. In 1962, he appeared in the "Bonanza" episode titled "The Decision", as a doctor sentenced to hang for the murder of a journalist. The judge in this episode was portrayed by John Hoyt, who later portrayed Dr. Phillip John Boyce, one of Leonard McCoy's predecessors, on the "Star Trek" pilot "". In 1963, he appeared in "The Virginian" episode "Man of Violence" as a "drinking" cavalry doctor with Leonard Nimoy as his patient (Nimoy's character did not survive). Perhaps not coincidentally, the episode was written by John D. F. Black, who went on to become a writer-producer on "Star Trek". Just before "Star Trek" began filming, Kelley appeared as a doctor again, in the "Laredo" episode "The Sound of Terror".