IV. c1 H highly effective in prolonging the life span of mice with advanced leukemia (L1210). 3 In our laboratories, these compounds have been found to inhibit the growth of the transplanted 6C3HED mouse lymphosar~ oma.~ It was thus of interest to prepare the corresponding 3'-fluoro (11) and 3', 5'-difluoro (111) derivatives of methotrexate (I) for evaluation as antineoplastic agents. Since the direct introduction of fluorine into the ...