Eight patients with childhood acute lymphoblastic leukemia (ALL) and hypercalcemia, osteopenia, or vertebral compression fractures seen at our institution during the last 12 years were evaluated for biochemical evidence of bone disease. Five patients were hypercalcemic, three had abnormal phosphorous levels, and four had elevated alkaline phosphatase values. Parathyroid hormone (PTH) was measured by a polyvalent radioimmunoassay in five patients and these levels were abnormally high in three patients. Four of these five patients also had PTH measured by a midregion-specific radioimmunoassay. One patient had a high PTH value. Two patients had low levels and one patient had a normal PTH level. Although these studies suggest diverse biochemical mechanisms may be contributing to the bone changes and hypercalcemia seen in childhood ALL, ectopic PTH production as well as ectopically produced fragments of PTH may have a role in mediating bone resorption and hypercalcemia.