The 1982 Aberdeen marathon race was held on a cool (12 degrees C) day on a flat, fast course. Fifty-nine of the 750 runners volunteered to take part in this study: rectal temperature of these competitors was measured within 5 min of completing the race. Venous blood samples were obtained before and immediately after the race; body weight of these subjects was also recorded before and after the race. During the race, 200 ml of fluid, either water or a glucose/electrolyte drink, was consumed at each of the seven feeding stations. The mean finishing time of the subjects was 221 +/- 37 min (mean +/- SD, range = 144-307 min). Post-race rectal temperature was 38.3 +/- 0.9 degrees C with a range of values from 35.6 degrees to 39.8 degrees C. The net weight loss was 2.02 +/- 0.72 kg equivalent to 2.9% +/- 0.8% of body weight. The correlation between post-race rectal temperature and finishing time (r = -0.234) was not statistically significant; post-race rectal temperature was significantly correlated with the time taken to complete the second half of the race (r = -0.348, P less than 0.01). No cases of heat illness were seen among the competitors. The results suggest that hypothermia rather than hyperthermia may be a problem for marathon runners competing under these conditions.