This investigation assesses the ability of the heat-dissipating system of the mouse to respond to equivalent heat loads (e.g., J/g) administered at varying intensities (e.g., J/g/s or W/kg). Use of a microwave exposure system provided a means to administer exact amounts of energy at varying rates in awake, free-moving mice. Male AJ mice were administered average heat loads of 12-13 J/g at rates of 19, 68, or 194 W/kg by exposure to 2,450 MHz microwave radiation while evaporative heat loss (EHL) was continuously monitored with dew-point hygrometry. The sensitivity of the EHL response was calculated as the heat dissipated by evaporation in response to microwave exposure divided by the heat absorbed. This ratio yields a dimensionless number that is related to the sensitivity of the EHL response and, in this study, is defined as the open loop gain (OLG) of EHL (i.e., motor response/error signal). When mice were exposed at an ambient temperature of 32.5 C to a specific absorption rate (SAR) of 19 W/kg, the OLG averaged 0.17; thus 17% of the absorbed heat was dissipated by EHL and the remaining 83% of the energy was passively dissipated.