Direct sequels to Tarzan of the Apes include The Return of Tarzan and The Beasts of Tarzan (1916). Twenty-one other adult Tarzan books appeared, the most interesting of which include Jungle Tales of Tarzan (stories); Tarzan and the Ant Men; and Tarzan and The Foreign Legion. Probably the last Tarzan book is Tarzan: The Lost Adventure (1996) compiled from notes that Burroughs left by Joe R. Lansdale. This Tarzan is in the dark spirit of the Burroughs sequels.

Here Tarzan is aided by Jad-bal-ja the lion and Nkima the chimp in defending a party of American archaeologists in search of the Lost City of Ur. He combats brigands, the savage inhabitants or Ur, and a mantis-like monster from the Earth's core — a reminder that Burroughs' Tarzan novels were as much science fiction as jungle adventure.