Between May 1987 and January 1991, 1354 patients, 1-21 years old, with standard or poor prognosis B-lineage acute lymphocytic leukemia were treated on the Pediatric Oncology Group Study 8602. One thousand three hundred and twenty-three patients entered remission and 1051 patients were randomized on day 43 to an intensification regimen containing L-asparaginase and intermediate-dose methotrexate (regimen B) or cytarabine and intermediate dose methotrexate (regimen C). After completion of intensification at week 25, all patients received the same maintenance therapy until 3 years from diagnosis. Overall 5-year continuous complete remission (CCR) for regimen B was 72+/-2% (s.e.) and for regimen C, 73+/-2% (P = 0.72 by log-rank analysis). Significant differences between treatments for CCR, testicular, CNS relapses overall or with regard to phenotype (pre-B vs early pre-B), gender, or race were not detected. During intensification, regimen C had significantly more bacterial infections (P = 0.05) and days spent in the hospital (P < 0.001) compared with regimen B, while regimen B had significantly more allergic reactions (P < 0.0001). No significant differences in CCR were noted between patients with pre-B and early pre-B ALL (P = 0.22 stratified by risk group and treatment). This study was unable to detect statistical difference between asparaginase (regimen B) and cytarabine (regimen C) during the intensification phase of therapy in children with B-lineage acute lymphocytic leukemia.