From June 1990 to February 1996, 35 patients with B-cell acute lymphoblastic leukaemia (B-ALL) 13 of whom had CNS disease and 28 patients with stage IV B-cell non-Hodgkin's lymphoma (B-NHL) 22 of whom had CNS involvement were treated with a short, intensive multiagent chemotherapy regimen (UKCCSG 9003 protocol) based on the French LMB 86 regimen. Fifty-five were boys. The age range was 11 months to 16.5 years (median 8.4 years). Chemotherapy included cyclophosphamide, vincristine, daunorubicin, high-dose methotrexate (COPADM) and etoposide/high-dose cytarabine (CYVE) with frequent intrathecal (i.t.) triple therapy (methotrexate, cytarabine and hydrocortisone). Cranial irradiation (24 Gy in 15 fractions) was recommended in patients with overt CNS disease. One patient with Wiskott-Aldrich syndrome was withdrawn after entry and has been excluded from the analysis. Ten patients (16%) have relapsed (CNS, four; BM, two; combined CNS and BM, three; and jaw, one) 4-11 months after diagnosis and two patients never achieved complete remission (CR). All have died. In seven of the patients who relapsed, treatment had been modified or delayed because of poor clinical condition. Seven patients (11%) died of toxicity 11 days to 4 months after diagnosis. The cause of death was sepsis (n = 5) or sepsis with renal failure (n = 2). With a median follow-up of 3.1 years from diagnosis (range 9 months to 6.3 years), 43 patients (69%) survive in CR. This study confirms the effectiveness of this regimen with regard to the relapse rate (16%), although the rate of toxic death is of concern.