U.S. Department of Defense studies to measure performance decrements associated with wearing chemical warfare (CW) protective combat clothing indicate that heat stress seriously degrades human performance. Even when heat stress is not a significant factor, performance of many combat, combat support, and combat service support tasks is degraded. In most field studies, many crews of combat units became operationally ineffective due to voluntary withdrawal of individual crewmembers. Many combined arms, field studies, and laboratory studies indicate that when CW-protective combat clothing is worn performance is seriously degraded for the detection of targets, engagement time, accuracy of fire, and manual dexterity tasks; and that a variety of psychological effects are created. Further, the degree of performance degradation varied with the tasks performed. Training in CW-protective combat clothing permits learning to modify procedures and consequently reduce negative effects, provided heat stress is not a significant factor. A growing body of evidence indicates there is inadequate training in the use of CW-protective combat clothing. A critical need exists for more and better training of skills needed under CW-conditions.