Resting oxygen consumption and total evaporative water loss were determined for N. alexis at ambient temperatures of 20, 28 and 33°C in dry air. The minimum rate of oxygen consumption was 0·61 ml min-1 at 33°C, and minimum total evaporative water loss was 4·75% body mass day-1 at 28°C. Respiration frequency, tidal volume and respiratory minute volume were determined for N. alexis at ambient temperatures of 20, 28 and 33°C in air of low or high relative humidity. Minimum values were obtained at 28°C and low RH for respiratory minute volume and tidal volume, and at 28°C and high RH for respiratory frequency. Expired air temperature of N. alexis at these temperatures was lower than or similar to ambient for mice in air of low RH, but was higher than or similar to ambient at high RH. Respiratory evaporative water loss, calculated from the previous data, was greatest for mice in dry air at 33°C, and least in moist air at 33°C. Cutaneous evaporative water loss made up about 40-60% of the total evaporative water loss for mice in dry air. The rates of total evaporative water loss were clearly reflected in the manner of body temperature regulation at high ambient temperatures. Hopping-mice in moist air at 28 and 33°C became hyperthermic, whereas mice in dry air showed only slight increases in body temperature. The significance of these data to hopping-mice in the field was discussed. © 1979 CSIRO. All rights reserved.