Several classical quinazoline analogues of folic acid bearing chloro or methyl substituents at position 5 were evaluated as inhibitors of the growth of four human gastrointestinal adenocarcinoma cell lines in vitro. The preparation of two of these, 5-chloro-5,8-dideazaisofolic acid, 1e, and 5-chloro-5,8-dideazaisoaminopterin, 2a, is reported for the first time. In addition, a new synthetic route to 5-chloro-5,8-dideazaaminopterin, 2b, is described. For compounds having a 2,4-diamino configuration, the presence of chlorine at position 5 afforded superior growth inhibitory potency. However, compound 1e was substantially less effective than its 5-methyl counterpart.