The purpose of the present study was to examine the effects of long term cold exposure on thermal responses and physical performance in men while wearing nuclear, biological and chemical (NBC) protective clothing. Six healthy men performed 60 min work/60 min rest cycles during 8 hours at an ambient temperature of -10 degrees C. Work was performed by stepping on a 20 cm high bench 15 times.min-1. Subjects were tested while wearing two different types of NBC clothing: impermeable rubber suit (IP) or semipermeable charcoal impregnated suit (SP) with cold weather underwear layers, as well as rubber gloves, boots and a full-face mask. During the tests oxygen consumption (VO2), rectal (Tre) and skin temperatures and sweat production were measured. Rectal and skin temperatures and body heat content followed the work/rest cycles in both types of NBC clothing. T(re) averaged 37.1 +/- 0.04 and 37.3 +/- 0.1 degrees C for IP and SP (NS), respectively. On average, mean skin temperature (Tsk) was 28.6 +/- 0.2 and 29.7 +/- 0.2 degrees C for IP and SP (p