Background Subjective assessment tools such as visual analog scales (VAS) or pain scores are commonly used to evaluate the intensity of chronic cancer-induced pain.However,their value is limited in some cases.We measured changes in VAS pain scores and salivary a-amylase (sAA) concentrations in cancer patients receiving radiotherapy for bone metastases to ascertain the correlation between these measures.Methods We enrolled 30 patients with bone metastases attending a single institution from June 2010 to March 2011.All patients with cancer-induced bone pain received radiation therapy (RT) at the same dose (30 Gy) and fractionation (3 Gy/ fraction,5 days/week) for palliative pain relief.We assessed heart rate (HR),systolic and diastolic blood pressures (DBP/SBP) and VAS pain scores before (d0) and after five (d5) and ten fractions (d10) of irradiation,sAA and salivary cortisol (SC)concentrations were measured using a portable analyzer and automated chemiluminescence analyzer,respectively.Results Radiotherapy markedly decreased VAS scores from (82.93±9.29) to (31.43±t16.73) mm (P ＜0.001) and sAA concentrations from (109.40±26.38) to (36.03±19.40) U/ml (P ＜0.001).Moreover,there was a significant correlation between these two indices (P ＜0.01,r=0.541).HR decreased by 6.5％ after radiotherapy,but did not correlate with VAS scores (P ＞0.05).SC concentrations and BP did not change significantly during the study (P ＞0.05).Conclusions The significant correlation between sAA concentrations and VAS pain scores identified in these preliminary results suggests that this biomarker may be a valuable,noninvasive and sensitive index for the objective assessment of pain intensity in patients with cancer-induced bone pain.