The effect of the currently fielded therapeutic antidotal (DRUG) combination (a cholinolytic, 2 mg of atropine sulfate, and an oxime, 600 mg of pralidoxime chloride) in combination with chemical protective Mission Oriented Protective Posture clothing (MOPP IV) was studied. Eight healthy male subjects participated in intermittent light physical activity (1.4-2.1 kcal/minute) in two distinct environments: 35 degrees C, 60% rh (95 degrees F, HOT) and 13 degrees C, 44% rh (55 degrees F, COOL). Subjects were exposed once to HOT wearing MOPP (CON) and once wearing MOPP after DRUG. Similarly, each subject was exposed to COOL wearing MOPP and MOPP after DRUG. Rectal temperature (Tre) and mean weighted skin temperature (Tsk) were not different between DRUG and CON during COOL. Exposure time during COOL was 350 minutes. Tre averaged .5 degrees C higher in DRUG than CON in HOT. The rate of core temperature increase was 2 times faster in DRUG than CON in HOT. Tsk was 1.0 degrees C higher in DRUG experiments in HOT. Whole-body sweating rate was 40% lower (p less than .05) in DRUG than CON experiments in HOT. Heart rate was 27 beats/minute higher by 30 minutes post-injection in DRUG at 35 degrees C. Exposure time was 213 +/- 30 minutes in CON and 190 +/- 38 minutes in DRUG at 35 degrees C. These data indicate the currently fielded therapeutic antidotal drug combination increases thermal strain in subjects exposed to a hot environment when wearing protective clothing. The results are applicable to subjects performing light, intermittent work. At higher work intensities, these findings of increased thermal strain would be exacerbated.