A number of nucleosides of 2-azaadenine (4-amino-7H-imidazo[4,5-d]-1,2,3-triazine) were prepared by a previously described route, and some of these were deaminated by means of adenosine deaminase. Alternatively, nucleosides of 2-azahypoxanthine (7H-imidazo[4,5-d]-1,2,3-triazin-4(3h)-one) were prepared from hypoxanthine nucleosides by a 2-azahypoxanthine (7H imidazo[4,5]-1,2,3-triazin-4(3H)-one) were prepared from hypoxanthine nucleosides by a ring-opening and reclosure sequence. The cytotoxicity of these compounds to human epidermoid carcinoma No. 2 cells in culture and to certain resistant sublines thereof was determined. 2-Azaadenine nucleosides chan be metabolized to nucleotides, the cytotoxic agents, by two pathways, but the activity of the 2-azahypoxanthine nucleosides appears to result only from cleavage back to 2-azahypoxanthine.