The incidence of torpor during summer and winter in response to cold exposure in Mops condylurus was studied in a subtropical environment. Body temperature changes under natural roosting conditions during winter and summer were monitored using bats fitted with temperature-sensitive radio transmitters. Rectal temperatures of free-roosting bats were also measured during winter. During summer, the effect of clustering on the incidence of torpor under different climatic conditions was investigated. Mops condylurus were thermolabile and displayed daily bouts of torpor during winter and summer, with body temperatures closely conforming to ambient temperatures. Body temperatures as low as 12.0°C were recorded during winter. Regression analysis showed a positive correlation between body and ambient temperatures in winter and summer. There was no difference in the incidence of torpor between single and clustering bats, although single bats maintained slightly higher body temperatures. Results indicate that M. condylurus maintained an optimally small T_b–T_a differential by readily becoming torpid under roosting conditions, thereby minimizing energy expenditure.