Giles' planigale (Plamgale gilesi) is among the smallest extant marsupials and inhabits deep soil cracks in arid floodplains We examined whether its physiology shows specific adaptations to its extreme habitat. Metabolic rate, body temperature, evaporative water loss and thermal conductance were measured for eight plamigales (average mass 9 g) exposed to four different ambient temperatures ranging from 10 degrees C to 32 degrees C. Water economy and respiratory variables were measured for the first time in this species. All of these standard physiological variables conformed to allometrically-predicted values for a marsupial All variables were significantly affected by ambient temperature, except tidal volume and dry thermal conductance Metabolic rate increased substantially at low ambient temperatures, as required to maintain a relatively constant body temperature of about 32-34 degrees C This increased oxygen demand was accommodated by increased ventilation rather than increased oxygen extraction Planigales had a comparatively high point of relative water economy of 191 degrees C. consistent with their small body size and arid habitat Torpor reduced energy expenditure by 79% and evaporative water loss by 62% Our study suggests that torpor use, along with behavioural adaptations, suffice for P Dies; to live underground in arid habitats without further physiological adaptations (C) 2010 Elsevier Inc All rights reserved