The series was never considered a money-maker for Ballantine, although the re-issue of several of its titles both before and after the series' demise shows that a number of individual works were considered successful. The Ballantines supported the series as long as they remained the publishers of Ballantine Books, but with their sale of the company to Random House in 1973 support from the top was no longer forthcoming, and in 1974, with the end of the Ballantines' involvement in the company they had founded, the series was terminated.