Localized cutaneous vasodilation (flush) is seen following systemic atropine administration. To verify calculated enhanced dry heat loss with actual changes in cutaneous blood flow, four men were studied in both control and atropine (0.025 mg.kg-1; im) experiments (Ta = 30 degrees C, Tdp = 7 degrees C) during moderate exercise (55% VO2 peak). Esophageal temperature (Tes) and arm sweating (ms) by local dewpoint were measured continously. Skin (forearm) blood flow (FBF) was measured twice each minute by venous occlusion plethysmography. Injection of atropine (2 mg) caused an increased sensitivity (+85%, p less than 0.01) in FBF to Tes with no change in the vasodilator threshold. An elevated Tes onset (0.3 degrees C, p less than 0.05) for sweating occurred with no change in the sensitivity of ms to Tes (-27%, p less than 0.20). No elevation in either forearm or Tsk occurred before the onset of vasodilation, however, both mean skin (Tsk) and local arm temperatures were higher in the atropine experiments after 15 min of exercise. Systemic atropine resulted in higher cutaneous vasodilation at the same core temperature with the local skin temperature following passively. The effect of systemic atropine in stimulation of increased cutaneous vasodilation is suggested to result by a combination of central and local responses which may be mediated through the release of vasoactive sustances.