The purpose of this research was to determine if fear is subject to the contrast effect that pervades psychophysical and other psychological phenomena. A contrast is said to occur when the judgement of a target stimulus is inversely related to the stimulus that preceded it; hence, it was expected that the response to a fearful stimulus should be inversely related to the response made to the preceding fear stimulus. The occurrence and nature of contrast effects were investigated in two laboratory studies of fearful people. In the first experiment, sixty-five university students were exposed on separate occasions to two fearful stimuli (spiders and snakes). The first exposure session was manipulated so that experimental groups differed in the amount of fear evoked by the stimulus (high fear, moderate fear, and low fear). Exposure to the second animal was designed to produce a moderate level of fear in all subjects. During exposure to the animals, measures of subjective fear and heart rate were taken. Results suggested that a contrast effect had occurred. Compared to a control group of subjects who experienced moderate fear on two occasions, subjects who had a high fear response to the initial stimulus showed a decrease in fear to the second stimulus. Subjects who had a low fear response to the initial stimulus showed an increase in fear to the second stimulus. This increase in fear was evident in subjective and physiological indices. None of the effects was evident when participants were reassessed one week later, suggesting that the fear contrast effect is transient. Four theories were evaluated with regard to their ability to account for the above findings. None of the theories could sufficiently explain the results, suggesting that a combination of at least two is necessary. The purpose of the second experiment was to replicate the above findings, and to investigate three additional aspects. These included: a) the participant's awareness of contrast effects, b) the role of perceived similarity of the context and target stimuli, and c) the interaction between mood states and prior context. A 2 by 3 factorial design was utilized with prior context (high fear, low fear) as the first factor, and mood induction (happy, sad and no mood induction) as the second factor. Subjective fear and heart rate were recorded during exposures to the feared stimuli. In addition, perceived similarity of the target and context was examined using three questionnaires, each assessing a different dimension of similarity. Awareness of contrasts was assessed with a post-experimental questionnaire. In the absence of mood induction, contrast effects occurred as they had in the first experiment. In the conditions involving mood induction, an interaction was evident. A happy mood blocked a low-to-moderate fear contrast, and a sad mood blocked a high-to-moderate fear contrast. Contrary to expectations, none of the similarity questionnaires was related to the magnitude of the contrast effect. Finally, subjects did not appear to be aware of their own experience of a fear contrast.