The Gray and McNaughton (2000) theory draws on a wide range of animal data to hypothesize that the emotions of fear and anxiety are separable. The authors tested their hypothesis in two studies. The first study examined associations between scores on questionnaire measures of fear, anxiety, and neuroticism; correlational analysis revealed that fear and anxiety are not interchangeable constructs. The second study examined associations between scores on questionnaire measures of fear/anxiety and performance in a military training setting; regression analysis revealed that fear captured significant variance in performance that was not shared with anxiety. These results imply that hypotheses derived from nonhuman animal data may hold important implications for understanding human emotion and motivation, especially in relation to fear and anxiety.