This study examined renal function in 42 children with acute lymphoblastic leukemia ( ALL) treated according to BFM-95 protocol. Fifteen ( group 1) were investigated longitudinally at 3 time points: before (T1), 4 weeks after (T2), and 2-6 months after (T3) consolidation therapy with high-dose methotrexate (HDMTX). The frequency of abnormalities in glomerular and tubular tests were nil at T1 and ranged from 13 to 40% at T2 and 7 to 33% at T3 in group 1. Twenty percent of the patients (n = 10) in group 2, who were examined at a single time point 7-36 months after consolidation, had glomerular and tubular abnormalities. There was only mild tubular abnormality in 5.8% of patients ( n = 17) in group 3, who were examined at a single time point a mean of 56.1 +/- 12.5 months after completion chemotherapy. These data show that consolidation therapy with HDMTX is frequently associated with acute renal toxicity in children with ALL but does not leave clinically significant late sequelae.