The Return of Doctor X (also billed as The Return of Dr. X) is a 1939 American science fiction-horror film directed by Vincent Sherman and starring Wayne Morris, Rosemary Lane, and Humphrey Bogart as the title character.

Despite supposedly being a sequel to Doctor X (1932), also produced by Warner Bros., the films are unrelated.

Flegg is initially unhelpful, but Garrett and Rhodes notice a striking resemblance between Flegg's strange assistant, Marshall Quesne and the late Dr. Maurice Xavier in old press cuttings.

Flegg admits using his new scientific methods to bring Xavier back from the dead and has employed synthetic blood to sustain his life.

A hunt begins for Quesne, who has discovered that Joan Vance, a nurse and Rhodes' sweetheart, is a carrier of the rare blood type.