A comparison was made between two personal auxiliary cooling approaches for the relief of thermal stress while wearing the standard USAF Chemical Defense Ensemble (CDE). Subjects exercised at approximately 40% VO2max in either warm (28/24/34 degrees C) or hot (38/26/43 degrees C) environmental conditions, (Tdb/Twb/Tbg degrees C, respectively). During each of three trials, four hours of intermittent work (four work/rest cycles) were attempted. Microclimate air cooling was applied in two different fashions and compared with a control trial during which no cooling was received (NC). In one trial, conditioned air cooling (Tin approximately 20 degrees Cdb) was delivered during rest periods only (intermittent cooling, IC), while during the second trial, ambient air cooling was also applied during the work period in addition to the conditioned air delivered during rest periods (continuous cooling, CC). During the warm condition, exposure cycle time was 45 min work and 15 min rest, while under the hot conditions, exposure cycle time was 30 min work and 30 min rest. Both CC and IC trials resulted in significantly extended work times, lower final rectal temperatures, heart rates, and sweat production (SP) than in the NC trial. Additionally, CC results in significantly lower SP, higher % sweat evaporation, and lower ratings of perceived exertion (RPE) and thermal comfort (TC) than IC at both warm and hot temperatures. Moreover, subjects were better able to maintain thermal equilibrium (i.e., cumulative heat balance) over time using CC compared to IC in the warm environment. The physiological significance of these findings, in some cases, was secondary to the improvement in subjective measures of TC and RPE.(ABSTRACT TRUNCATED AT 250 WORDS)