4-Alkylcytosine nucleosides 2 were prepared by nucleophilic substitution of the 4-(1, 2, 4- triazol-l-y1) residue of uracil nuc-leoside derivatives 1 using different amino compounds. The antitumor activity against L1210 murine leukemia of fifteen 4-alkylcytosine nucleosides dissolved in buffer or incorporated into liposomes was tested. Liposomal l-(PD-arabinofu- ranosyl)-4-octadecylamino-2 (lH)-pyrimidinone (2d) having the highest activity gave an ...