1539 The independence of body core temperature (Tc), across a wide range of ambient conditions is well established. However, such independence implies little influence of heat-transfer attributes of the individual, such as surface area to mass ratio, on thermoregulation. This investigation examined whether exercising Tc is independent of an individual's ability to dissipate heat, and whether this independence is sustained during uncompensable heat stress. Eighteen males were recruited to obtain a broad range of individual characteristics: peak oxygen consumption (34.1-78.3 ml/kg/min, range), sum of eight skinfolds (46.5-232.0 mm), surface area (1.7-2.2 m2), mass (62.4-102.1 kg), surface area to mass ratio (0.0218-0.0275 m2/kg), endurance training history (0-680 min/week). Subjects completed three, 30-min exercise trials, cycling semi-clothed, at 15.1°C (82% RH), 28.1°C (55.2% RH) and 40.0°C (35.5% RH), at relative intensities of 25% (WL1), 40% (WL2), and 55% (WL3) peak aerobic power, respectively. Tc was measured from the oesophagus (Tes) and rectum (Tre). WL3 at 40°C was analysed separately, as it appeared uncompensable in all subjects. There was a main effect of air temperature on Tes (p<0.05), but no interaction with time (within workloads; p>0.05). Of the individual characteristics investigated, none correlated with resting or exercising steady state Tes or Tre (p>0.05). The highest correlation with Tes was for body mass, explaining only 5% (p=0.38) of the variance in Tes. However, during uncompensable heat stress, body mass, surface area, surface area to mass ratio and adiposity all had significant correlations with changes in Tes (p<0.05). Differences in initial Tc resulted in an offset throughout exercise, and hence a rise in Tc which was independent of air temperature. Also, despite vastly different abilities to dissipate heat, the same change in Tc resulted. Subsequently, theoretical advantages of various morphological characteristics, are of limited significance when the heat stress is compensable. However, during uncompensable heat stress, these characteristics influence Tc.