The functional properties of hemolysates from the bats Rhinolophus ferrumequinum, Miniopterus schreibersi and Pipistrellus pipistrellus were studied at 25 degrees C and 37 degrees C over the pH range 7.0-7.4. The concentrations of 2,3-DPG and their effect on hemoglobin O2 affinity were also studied under the same conditions. At pH 7.4 and 37 degrees C hemoglobin O2 affinity was higher than in similarly-sized non-flying, normothermic mammals. The Bohr effect values in the three bat species were slightly lower than those reported for small non-flying mammals. The temperature sensitivities of the oxygenation reactions in bat hemoglobins were low, which may be a mechanism for avoiding the effects of abrupt body temperature changes on oxygen loading and unloading by hemoglobin. The levels of 2, 3-DPG high in red blood cells of active bats decrease when the bats are hibernating. Thus changes in hemoglobin O2 affinity are more probably due to changes in 2,3-DPG concentrations than to alterations of body temperature.