Two protocols were used to discover whether the reflex response in skin blood flow (SkBF) to rising skin temperature (Tsk) was dependent on the level of internal temperature. Part I. In five subjects, Tsk (controlled with water-perfused suits) was raised to 37 degrees C prior to, between 2 and 5 min, or between 10 and 17 min of exercise. The associated SkBF elevation per degree rise in Tsk averaged 0.20, 1.28, and 1.75 ml/100 ml . min, respectively. When Tsk was raised during the first 5 min of exercise, esophageal temperature (Tes) rose markedly (0.39 degrees C), but transiently fell if Tsk was raised after 10 min of exercise. Part II. In six subjects, different work loads were used to develop different levels of internal temperature. Tsk was elevated to 37 degrees C after 10--15 min at light (50--75 W) or moderate (100--150 W) work loads. At the heavier work load (and higher Tes), the rise in forearm SkBF per degree rise in Tsk averaged 2.33 +/- 0.38 (SE) times that observed at the light work load. These data strongly suggest that the reflex response of SkBF to rising Tsk is dependent on the level of internal temperature.