We measured the levels of carboxyterminal propeptide of type I procollagen (PICP), cross-linked carboxyterminal telopeptide region of type I collagen (ICTP) and carboxyterminal parothyroid hormone-related protein (C-PTHrP) in serum of patients with hematological malignancies. ICTP and C-PTHrP levels in serum of multiple myeloma (MM), non-Hodgkin's lymphoma (NHL) and adult T-cell leukemia (ATL) patients with bone lesions and hypercalcemia were significantly higher than those of patients without bone lesions and hypercalcemia. ICTP and C-PTHrP levels in ATL were significantly higher than in MM and NHL. There was a correlation between ICTP and C-PTHrP in serum of ATL patients, but no correlation in MM and NHL. Serum ICTP levels tended to correlate with serum beta 2-microglobulin and survival in patients with MM. Therefore, ICTP and C-PTHrP levels in serum may be useful in the diagnosis of bone lesions and hypercalcemia in hematological malignancies. In particular, ICTP may be a useful bone resorption marker in MM.