The pharmacokinetics of N4‐behenoyl‐1‐β‐D‐arabinofuranosylcytosine (BHAC), a lipophilic antitumor analog of 1‐β‐D‐arabinofuranosylcytosine (ara‐C), was investigated, by assay of plasma and leukemic cells of ten acute leukemic patients receiving 60‐minute intravenous (IV) infusion of 700 mg/m2BHAC, for BHAC and 1‐β‐D‐arabinofuranosylcytosine 5′‐triphosphate (ara‐CTP) by high‐performance liquid chromatography, ara‐C by radioimmunoassay, and 1‐β‐D‐arabinofuranosyluracil (ara‐U) by gas chromatography‐mass fragmentography. The plasma concentration of BHAC reached a maximum (173.4 ± 75.3 μg/mL) at the end of the infusion and then declined in a biphasic pattern with an initial‐phase half‐life (t1/2α) of 1.00 ± .36 hours and a second‐phase half‐life (t1/2β) of 4.28 ± 2.35 hours. That of ara‐C similarly reached a maximum (102.2 ± 39.9 mg/mL) at the end of the infusion and then declined with t1/2α of 1.37 ± 1.11 hours and t1/2β of 11.2 ± 4.31 hours. Intracellular ara‐CTP concentration increased in a linear‐accumulation manner for the first 4 hours after the infusion, reached a maximum of .081 ± .112 μg/107cells at approximately 7 hours, and then declined very slowl