Drs. Takimoto and Allegra present a comprehensive overview of the development of antifolates over the past decade and a half. The antifolates are antimetabolite antineoplastic agents that are structurally and chemically similar to naturally occurring folates required for the synthesis of purines and pyrimidines. These drugs interfere with DNA synthesis by inhibiting key enzymes. They are transported across the plasma membrane and converted intracellularly to cytotoxic species, which must compete with endogenous substrates for target enzyme binding.