Objectives: In this study, we aimed to investigate the bone turnovermarker levels according to bisphosphonate usage and radiotherapy(RT) in cancer patients with metastases in osteolytic pattern. Patients and methods: A total of 52 patients (13 males, 39 females;median age: 52 years; range, 37 to 78 years) treated with RT forosteolytic bone metastases between April 2005 and April 2006were retrospectively analyzed. Bone-specific alkaline phosphatase(BAP), amino-terminal cross-linked telopeptide of type I collagen(NTX-I), amino-terminal propeptide of type I procollagen (PINP),osteocalcin (OC), deoxypyridinoline (DPD), pyridinoline (PYD),alkaline phosphatase (ALP), creatinine, calcium (Ca), phosphate (P),magnesium (Mg), and 24-h urine Ca levels were measured in blood andurine before the initiation of RT, six weeks and six months after RT. Results: A decrease in BAP, PINP, and creatinine levels wasobserved after RT (Week 6 p=0.006, Month 6 p=0.008). Sixteenpatients who already used bisphosphonate before RT were excludedfrom statistical calculation. The remaining 36 patients who weretreated with bisphosphonate after the first blood test were evaluatedseparately. In this group of patients, BAP, PINP, NTX, creatinine, andCa levels significantly increased at six weeks after RT. The PINP andcreatinine values significantly decreased at six months after RT. Thevariation between two different RT arms was assessed with repeatedmeasures variance analysis. There was a statistically significantdifference for NTX, OC, and creatinine levels between the first andsecond measurements. Conclusion: Radiotherapy is an effective method in the treatmentof osteolytic bone metastases. Bone turnover markers can providean objective evaluation on RT response and parallel to imagingmodalities criteria for evaluation. Bisphosphonates may alter thelevels of these indicators. However, in this study, there were nostatistically significant differences between the levels of markers fortwo different RT schedules.