To investigate the effects of disease and intensive chemotherapy on bone turnover and growth in children with acute lymphoblastic leukemia (ALL), a longitudinal prospective study was carried out in 22 children, aged 1.2-13.5 yr, enrolled in the Medical Research Council-funded randomized trial of childhood ALL treatment in the UK. We measured lower leg length and markers of bone formation [bone alkaline phosphatase (ALP) and procollagen type I C-terminal propeptide (PICP)], bone resorption [pyridinoline, deoxypyridinoline, and carboxyl-terminal telopeptide of type I collagen (ICTP)], soft tissue turnover [procollagen type III N-terminal propeptide (P3NP)], and the GH axis [IGF-I, IGF-binding protein-3 (IGFBP-3), IGFBP-2, and urinary GH] at 1- to 4-week intervals from diagnosis to week 27 of treatment. In addition, GH-binding protein was measured at diagnosis. At diagnosis, mean SD scores were: bone ALP, -1.84; PICP -1.77; pyridinoline, -1.42; deoxypyridinoline, -1.66; ICTP, -0.42; P3NP, +1.45; GH, +24.4; IGF-I, -1.70; IGFBP-3, -0.88; IGFBP-2, +2.42; and GH-binding protein, -0.69. Bone ALP, PICP, and IGFBP-3 were all correlated (P < or = 0.03). During induction and intensification, there was shrinkage of the lower leg, with decreases in PICP, pyridinoline, ICTP, and P3NP (P < 0.05), whereas IGF-I and IGFBP-3 increased (P < 0.05). After prednisolone was discontinued, bone ALP and collagen markers increased markedly (P < 0.01), but there was no significant change in IGF-I and IGFBP-3. In 12 children who received high dose i.v. methotrexate, postglucocorticoid increases in bone ALP and PICP were less, whereas those in ICTP and P3NP were greater, compared to levels in children who did not receive methotrexate (P < 0.05). We conclude that ALL itself caused GH resistance and low bone turnover. During early intensive chemotherapy, further suppression of osteoblast proliferation and osteoclast activity occurred, not mediated through the systemic GH axis, probably by the direct action of prednisolone on bone. The postglucocorticoid increase in bone turnover was also independent of the GH axis and was modulated by high dose i.v. methotrexate, which depressed osteoblast recovery and enhanced osteoclast activity.