Phobic individuals expect aversive UCS's following encounters with phobic stimuli. Previous research using a thought-experiment procedure showed that contamination rather than harm-related outcome expectancies differentiated best between high and low spider fearful undergraduates. This study investigated the alleged role of these UCS-expectancy biases in the maintenance of phobic complaints. First, this study sought to replicate these earlier findings in a community sample of high spider fearful individuals who applied for treatment (n = 60) and a sample of low spider fear controls (n = 30). Second, the present study tested if UCS-expectancies disappear following successful treatment and whether there were any differences between harm and contamination-related UCS expectancies in this respect. If contamination-and/or harm-related UCS-expectancy biases play a critical role in the maintenance of spider fear, these biases should be substantially reduced after successful treatment. The results showed that spider fearful individuals associated spiders relatively strongly with both harm-and contamination-related outcomes. Consistent with the alleged reciprocal relationship between phobic fear and UCS expectancy bias, both types of biased expectancies were effectively reduced following treatment.