The effects of intramuscular saline (control), atropine (2 mg), and/or pralidoxime (600 mg) on heat exchange was evaluated in four healthy males during seated, cycle exercise (55% Vo2 peak) in a temperate environment (Ta = 30.3 degrees C, Pw = 1.0 kPa). Esophageal (Tes), rectal (Tre), and mean skin temperatures (Tsk), and chest and forearm sweating (ms) were continuously measured. Skin blood flow (FBF) from the forearm was measured twice each minute by venous occlusion plethysmography. Whole body sweating was calculated from weight changes. The expected result of atropine injection, decreased eccrine sweating (-60%, p less than 0.05) and elevated esophageal (+0.4 degree C, p less than 0.05) and skin temperatures (+2.1 degrees C, p less than 0.05) was observed relative to control. Heart rate (+28 b X min-1) and FBF (+9 ml X 100 ml-1 X min-1) were higher after atropine. Pralidoxime, in general, did not affect the core and skin temperature responses to the exercise differently from control; however, a slightly elevated FBF (+3 ml X 100 cc-1 X min-1, 33%) compensated for the reduction in whole body sweating (-45%, p less than 0.05] that we observed. The combination of the drugs resulted in significantly higher esophageal (0.4 degree C) and skin (0.9 degree C) temperatures than atropine alone, as has been previously shown. The thermoregulatory disadvantage of inhibited sweating by atropine was partially compensated for by enhanced skin blood flow in this environment where Ta less than Tsk. Pralidoxime was shown to decrease whole body sweating, by a mechanism as yet unexplained.