To test if magnitudes of the beneficial actions of CO water bath therapy on blood flow and vascular density are dependent upon temperature, ischemia in the hind limb of rats was induced by occluding the left femoral artery for 2 weeks and the animals were exposed to water bath therapy with or without CO at 34 or 41 °C for 4 weeks (20 min treatment each day for 5 days/week). CO water bath therapy at 34 °C increased peak, minimal, and mean blood flow by 190%-600% in the ischemic limb. On the other hand, CO water bath treatment at 41 °C increased these parameters of blood flow by 37%, 55%, and 41%, respectively, in the ischemic limb. The small blood vessel count, an index of vascular density, in the ischemic limb was increased by CO water bath therapy at 34 and 41 °C by 32% and 122%, respectively. No changes in the ischemic animals by CO water bath therapy at 34 or 41 °C were observed in the heart rate, R-R interval, and plasma lipid or glucose levels. These data indicate that the beneficial effect of CO water bath therapy at 34 °C on blood flow in the ischemic muscle is greater whereas that on vascular density is smaller than changes in these parameters at 41 °C.