A series of clinical pharmacokinetic and pharmacodynamic studies of anticancer drugs has been conducted in children with cancer. Since these drugs typically have narrow therapeutic indices, frequently producing toxicities at dosages required for therapeutic effects, they represent an exemplary class of drugs for pediatric pharmacodynamic studies. Reviewed herein are pediatric pharmacokinetic studies of teniposide and high-dose methotrexate, which demonstrate age-related differences in the disposition of these two highly active anticancer drugs, and pharmacodynamic studies which demonstrate a relation between the disposition of these drugs and their clinical effects (efficacy and toxicity) in children with acute lymphocytic leukemia.