Twenty female subjects were selected from a larger subject pool on the basis of their scores to the 'snakes' item on the Geer (1965) Fear Survey Schedule. Ten of the subjects were selected as phobic; the other ten were non-phobic controls. Heart rate, skin conductance and self-reports of fear and imagery vividness were continuously monitored while subjects repeatedly imagined a prescribed snake scene for a total of 15 trials. The phobic group reported more overall fear to the images. Further, while the nonphobic subjects reported progressively less fear over trials, the phobic subjects reported progressively more fear. The groups did not differ in rated imagery vividness. However, heart rate responses to the image differentiated the two groups. The non-phobic subjects showed a progression from cardiac acceleration in the early trials to a biphasic response pattern, deceleration preceding acceleration, in the later trials. In contrast, the phobic subjects demonstrated sustained acceleration in the later trials. The groups did not differ in skin conductance response amplitude. © 1979.