The aim of this study was to assess the effect of arm exercise on the heat balance in spinal cord-injured (SCI) individuals with complete lesions at ambient temperatures of 10 and 35 degrees C. Four SCI with a high lesion (> or = T6) (SCI-H), seven with a low lesion (< T6) (SCI-L), and ten able-bodied controls (AB) performed arm-cranking exercises at 40 % of the maximal power output for 45 min, once in 10 degrees C and once in 35 degrees C. Oxygen uptake, rectal temperature, and skin temperature (chest, upper arm, thigh, calf) were measured at rest and 15, 30, and 45 min after the onset of exercise. Metabolism, heat production, skin temperature, mean body temperature (a combination of rectal and skin temperature), and body heat content were calculated. Heart rate at 10 degrees C was 103 b/min in SCI-H, 120 in SCI-L and 112 in AB, while in 35 degrees C, heart rate was 112 b/min in SCI-H, 144 in SCI-L and 134 in AB. The increase in rectal temperature in 35 degrees C was larger in SCI-L (+ 0.07 degrees C) and SCI-H (+ 0.08 degrees C) than in AB (+ 0.06 degrees C). The decrease in mean body temperature at 10 degrees C was larger in SCI-H (33.0 +/- 0.68 degrees C) than in SCI-L (33.6 +/- 0.29 degrees C) and AB (34.5 +/- 0.31 degrees C). During exercise in 35 degrees C, mean body temperature increased in all three groups. The increase in body temperature in SCI-L was larger than in AB. During exercise in 10 degrees C, body heat content decreased in SCI-H (80.0 +/- 15.1 kJ) and SCI-L (89.2 +/- 9.1 kJ) but remained constant in AB (97.0 +/- 16.1 kJ). During exercise in 35 degrees C, body heat content increased in all three groups. The increase in body heat content after exercising in 35 degrees C was not significantly different between the three groups. In summary, mean body temperature and body heat content in the cold decreased in SCI, despite exercising. In the heat, mean body temperature and body heat content seems to increase more in SCI than in AB. We can conclude that SCI are at a greater risk for a disturbed heat balance during exercise in the cold and in the heat than AB. Both in the cold and in the heat, precautions should be taken even earlier and be more intensive for SCI than for AB.