In seeking analogues of cyclophosphamide (1) having improved antitumor activity by virtue of accelerated formation of the cytotoxic metabolite phosphoramide mustard, cis and trans isomers of 5-fluoro-and 5-chlorocyclophosphamide (9, 10, 11 and 12, respectively) were synthesized by condensation of the appropriate 3-amino-2-halopropan-1-01 (13 or 26) with N, N-bis (2-chloroethyl) phosphoramidic dichloride (14). The metabolism of the ...