Two metabolites of N4-behenoyl-1-beta-D-arabinofuranosylcytosine (BH-AC) were found in the plasma and urine, and a hydrolytic product, arabinosylcytosine (ara-C) and its deaminated product, arabinosyluraci (ara-U), were found in a preclinical study using monkeys. Of a given dose, 96% was found as ara-U and 3% as ara-C in urine in 24 h. The plasma disappearance curve of BH-AC is biphasic; the half-life of the initial phase is 40 min and that of the second phase is 120 min. At 8 h the BH-AC level is 21.9 micrograms/ml and falls exponentially to 3.6 micrograms/ml by 12 h. Ara-C was detected at the levels of 0.4-0.6 microgram/ml for 4 h. Comparative data of pharmacokinetic parameters among BH-AC, ara-C, and O2,2'-cyclocytidine showed that BH-AC had the longest plasma half-life, the smallest elimination-rate constant and the smallest excretion-rate constant. The plasma-clearance study of BH-AC in 13 patients showed essentially a pattern similar to that in monkeys; the plasma t 1/2 of 60 min in the first phase and of 180 min in the second. The BH-AC level at 2 h is 15.4 micrograms/ml, and 1.8 microgram/ml at 8 h. Initial phase I study of BH-AC was evaluated in 14 patients with leukemia and other malignancies. The starting dose was 1.5 mg/kg given as a single IV infusion for 3. The doses were when escalated up to 5.0 mg/kg. No side effects were noted with a single dose schedule. Daily consecutive infusions of 2.0 mg/kg-6.0 mg/kg for 4-21 days resulted in two patients having nausea, two anorexia, and one developing skin eruptions. Significant hematologic effects were noted with the daily infusion. One patient with acute myeloblastic leukemia achieved complete remission with 5.0 mg/kg BH-AC given daily for 21 days. It pharmacologic features, minimal toxicity, and the capability of inducing complete remission in acute leukemia indicate that BH-AC undoubtedly deserves further prospective clinical trials.