In a 1976 interview, Dick said he planned to write a sequel novel to The Man in the High Castle: "And so there's no real ending on it. I like to regard it as an open ending. It will segue into a sequel sometime." Dick said that he had "started several times to write a sequel", but progressed little, because he was too disturbed by his original research for The Man in the High Castle and could not mentally bear "to go back and read about Nazis again." He suggested that the sequel would be a collaboration with another author: "Somebody would have to come in and help me do a sequel to it. Someone who had the stomach for the stamina to think along those lines, to get into the head; if you're going to start writing about Reinhard Heydrich, for instance, you have to get into his face. Can you imagine getting into Reinhard Heydrich's face?"
Two chapters of the proposed sequel were published in The Shifting Realities of Philip K. Dick, a collection of his essays and other writings. The chapters describe Gestapo officers reporting to Nazi Party officials about their time-travel visits to a parallel world in which the Nazi conquest has failed, but which contains nuclear weapons, available for the stealing by the Nazis back to their world. A working title for the novel, describing the emergence of a hybrid Japanese–American culture, was Ring of Fire.
On occasion, Dick said that 1967's The Ganymede Takeover began as a sequel to The Man in the High Castle, but that it did not coalesce as such. Specifically, the Ganymedans occupying the Earth began as the Imperial Japanese occupying the conquered US. Dick's novel Radio Free Albemuth also is rumored to have started as a sequel to The Man in the High Castle. Dick described the plot of this early version of Radio Free Albemuth—then titled VALISystem A—writing: "... a divine and loving ETI [extraterrestrial intelligence] ... help[s] Hawthorne Abendsen, the protagonist-author in [The Man in the High Castle], continue on in his difficult life after the Nazi secret police finally got to him... VALISystem A, located in deep space, sees to it that nothing, absolutely nothing, can prevent Abendsen from finishing his novel." The novel eventually evolved into a new story unrelated to The Man in the High Castle. Dick ultimately abandoned the Albemuth book, unpublished during his lifetime, though portions were salvaged and used for 1981's VALIS. The full book was published in 1985, three years after Dick's death.