Exposure to an open-field is psychologically stressful and leads to an elevation in core temperature (T_c). This increase in T_c during open-field exposure is usually referred to as stress-induced hyperthermia and can be blocked centrally with cyclooxygenase inhibitors such as sodium salicylate and indomethacin. Methyl scopolamine (MS), a peripheral muscarinic antagonist, and pyridostigmine (PYR), a peripheral carbamate that inhibits acetylcholinesterase, do not cross the blood brain barrier and have little effect on T_c in resting, non-stressed animals. However, we have found that MS has an antipyretic effect on T_c caused by handling and cage switch stress. PYR has been found to have minimal effects of temperature regulation. PYR should act pharmacologically to reverse effects of MS. To this end, we assessed the effects of MS and PYR on SIH. Male Sprague Dawley rats at 90 days of age were housed individually at an ambient temperature (T_a) of 22 °C. T_c and motor activity were monitored by radiotelemetry. The open field chamber consisted of an illuminated Plexiglass box (61 x 61 x 61 cm) maintained at a T_a of 22 °C. Rats were dosed intraperitoneally (ip) at 1200 hr with 1.0 mg/kg MS, 0.1 mg/kg PYR, a combination of MS and PYR, or saline and placed immediately inside the open field chamber for 60-min. T_c of controls increased by 1.7 °C during open field exposure. Stress-induced hyperthermia was suppressed immediately by MS and enhanced by PYR. T_c only increased by 0.3 °C in the MS treated animals. The hyperthermic response in the PYR group was nearly 0.6 °C above that of rats dosed with saline. Co-administration of PYR and MS led to a stress-induced hyperthermia response nearly identical to that of rats injected with saline. Overall, open-field stress exacerbated the effects of MS and PYR on body T_c. These data support a peripheral cholinergic mechanism that mediates stress-induced hyperthermia in the male rat.