Fazarabine (Ara-AC), a structural analog derived from the antitumor nucleoside cytosine arabanoside (Ara-C) and 5-azacytidine (5-AC), was studied in a phase I clinical trial. Doses ranging from 0.2 to 2.0 mg m-2 h-1 were given intravenously over 72 h every 28 days. The maximum tolerated dose (MDT)