The increased use of high-dose cytarabine in the treatment of neoplasms prompted this study on the reconstituted stability of cytarabine in intravenous admixtures with sodium bicarbonate and in plastic syringes. The study of the effect of sodium bicarbonate was prompted by the frequent use of this agent in patients being treated with cytarabine as a means of achieving systemic alkalinization in order to manage hyperuricemia. The stability of reconstituted cytarabine in plastic syringes was measured to determine whether cytosine arabinoside could be reconstituted and stored prior to use. The results of this study indicate that sodium bicarbonate 50 mEq/L in the intravenous solution containing cytarabine has no effect on the chemical stability of cytarabine for at least one week at room temperature or in the refrigerator. Consequently sodium bicarbonate and cytarabine can be coadministered in one intravenous solution. The reconstituted stability of cytarabine at 20 mg/ml and 50 mg/ml is not affected by storage in plastic syringes.