In 1959, Ballantine Books was looking for something to replace its successful line of "Mad" mass-market paperback reprints after Gaines had taken it to another publisher. Ballantine had earlier published "The Humbug Digest" in the same format, though it fared poorly in the market. Kurtzman proposed a book of original material designed for the format, which Ian Ballantine, with reservations, accepted on faith out of respect for Kurtzman. "Harvey Kurtzman's Jungle Book" was the first mass-market paperback of original comics content in the United States, and to Kurtzman biographer Denis Kitchen was a precursor to the graphic novel. Whereas his "Mad" stories had been aimed at an adolescent audience, Kurtzman made "Jungle Book" for adults, which was unusual in American comics. "Jungle Book" sold poorly, but remained a favorite among its small number of devoted fans. If it had been a success, Kurtzman intended to continue with more books in the same vein.