OBJECTIVE: To determine if football (FB) players and cross-country (CC) runners had different thermal responses to their respective training sessions. DESIGN AND SETTING: On days 4 and 8 of preseason training, we assessed core (T(c)) and skin (T(sk)) temperatures. SUBJECTS: Fifteen collegiate athletes volunteered: 10 FB players (age = 21.2 +/- 1.14 years, height = 193.5 +/- 4.8 cm, mass = 116.6 +/- 16.3 kg, and V(2max) = 44.7 +/- 9.4 mLkg(-1)min(-1)) and 5 CC runners (age = 22.8 +/- 2.77 years, height = 176.3 +/- 8.9 cm, mass = 71.16 +/- 8.9 kg, and V(2max) = 71.3 +/- 6.18 mLkg(-1)min(-1)). MEASUREMENTS: We measured T(c) using ingestible sensors before, during, and immediately after exercise. The T(sk) was measured at the calf, forearm, back, chest, and forehead sites. Level of dehydration was assessed by urine specific gravity. RESULTS: Mean wet-bulb temperature was 74 degrees F (23.33 degrees C). Resting T(c) in shorts and T-shirts was higher in the FB group. The T(c) midway through practices and runs was higher in the CC and FB subjects when active, compared with the FB subjects when inactive. Postexercise T(c) was higher in the CC group than the FB group with pads, and postconditioning T(c) was higher in the FB subjects with pads versus no pads. Forehead, chest, back, and mean weighted T(sk) were higher in the FB group. The T(c) and urine specific gravity were not correlated. CONCLUSIONS: The T(c) fluctuated in the FB subjects during practice depending on exercise intensity, whereas T(c) increased steadily in the CC subjects during continuous running. Thus, CC athletes may have to decrease intensity to maintain thermoregulation. Our FB players seemed to dissipate heat adequately during rest periods.