The pharmacokinetic behavior of vincristine in pediatric patients has not been well characterized. The present study will obtain detailed information on vincristine pharmacokinetics in patients being treated for standard risk ALL according to or on CCG protocols 1952/1962/1991. A limited sampling strategy will be developed, and the interpatient and intrapatient variability of vincristine pharmacokinetics in children will be studied. A correlation between vincristine neurotoxicity and vincristine pharmacokinetics will be sought.