The present study investigated the relationship between deductive reasoning and phobic fear: In the first experiment, we succesfully evaluated a reasoning paradigm that was specifically designed to index inteference effects of prior beliefs. Forty-two female undergraduates were presented with a series of syllogisms varying in believability and logical validity and were asked to judge the syllogisms' logical validity. Participants were relatively fast when there was a match and relatively slow when there was a mismatch between believability and validity (belief bias). In Experiment 2, participants were 31 spider-phobic women and 27 nonfearful women. They were presented with two types of syllogisms. One category of syllogisms was concerned with neutral themes and the other with phobia-relevant themes. Again, participants showed a belief bias. This bias was especially strong in the phobic group. Yet the enhanced belief bias in phobic women was not specific for phobic material, The results support the view that phobic subjects are characterized by a general tendency to confirm rather than to falsify prior beliefs.