3-Deazauridine (3-DAU) pharmacology was studied in 20 patients who received the drug by rapid or continuous infusion. In 8 studies, the plasma clearance of 3-DAU after rapid administration was biphasic, with an average terminal t1/2 of 4.4 hr and an extrapolated volume of distribution of 0.57 liter/kg. After 5-day continuous infusion of 3-DAU, the plasma clearance was also biphasic, with an average terminal t1/2 of 21.3 hr and an extrapolated volume of distribution of 18.8 liter/kg. 2,4-Dihydroxypyridine, the aglycone of 3-DAU, was observed in plasma but not in urine of patients receiving the drug by rapid infusion. The urinary excretion of 3-DAU was low, only 7.8% 24 hr after rapid infusion and 7.2% up to 4 days after continuous infusion. Tissue distribution of 3-DAU was determined from autopsy samples of 2 patients. Not only were high levels of 3-DAU detected in the tissues studied, but 3-DAU triphosphate, the active metabolite of 3-DAU, was present in brain, lung, and liver.