The aim of this study was to determine if 6-month acclimation would enable accurate evaluation of hematological, biochemical data, and ECG recorded under restraint for conscious rhesus monkeys of both sexes. Periodic evaluation of these parameters was made during the 6-month period of acclimation. The platelet count, alkaline phosphatase, glucose, and sodium levels significantly decreased, whereas creatinine increased, compared with pre-acclimation values. The heart rate was significantly reduced compared with pre-acclimation values. QT-RR relation followed the square root regression function, which means modification of Bazett's QTc formula can be applied even if the ECG is recorded under restraint. In conclusion, 6-month acclimation was effective for stabilizing the blood data and for allowing accurate evaluation of the ECG even under restraint. Current results show that an acclimation period at least 3 months may be necessary prior to using rhesus monkeys for chronic studies.