The antitumor activity of 5-aza-2′-deoxycytidine (5-aza-dCyd), a nucleoside analog, was established in human head and neck cancer xenografts, transplanted in nude mice. A significant response was noted in 3 of 5 lines, when the drug was injected intraperitoneally at a maximum tolerated dose of 2 mg/kg every four days for three doses. In two most sensitive lines 1 out of 6 tumors regressed completely. The antitumor activity of the drug may depend on the schedule used, as illustrated by the fact that just one of these two lines appeared to be sensitive when treated with low daily doses (0.25 mg/kg). One of the two sensitive lines also responded to the treatment with low daily doses (0.25 mg/kg). In two lines, 5-aza-dCyd showed equal or better antitumor activity when compared to the conventional drugs known to produce remissions in patients with head and neck cancer (cisplatin, methotrexate, bleomycin, 5-fluorouracil and cyclophosphamide). 5-Aza-dCyd is a drug with potential value in the chemotherapeutic treatment of patients with head and neck cancer.