Previous research on category activation effects demonstrates that extreme exemplar priming can lead to contrast effects as well as assimilation effects in target judgments. Two experiments extended this line of research by investigating the moderating role of perceived comparability, that is, the extent to which the exemplar and target are believed to belong to the same category and thus can be compared. In both experiments, participants judged the speed of a person displayed on a picture following priming with animals exemplifying either extreme speed (‘cheetah’) or extreme slowness (‘turtle’). In addition, in the second experiment a behavioural measure was included. In the first experiment individual differences concerning the perceived comparability between animals and humans were assessed. In the second experiment perceived comparability was experimentally varied. Results showed that the direction of category activation effects (i.e. assimilation versus contrast) depended on the extent to which the prime and target categories were seen as comparable. Contrast effects on both judgments and behaviour emerged when the prime and the target category were perceived as comparable. However, assimilation effects on judgment and behaviour ensued when the prime and target category were not perceived as comparable.