This article investigates two competing explanations of the mere exposure effect - the cognition-based perceptual fluency/misattribution theory (PF/M) and the affect-based hedonic fluency model (HFM) - under incidental exposure conditions. In two studies, the classical mere exposure effect is replicated in the context of banner advertising. The findings rule out the cognition-based PF/M and suggest that the spontaneous affective reaction resulting from perceptual fluency is a crucial link between fluency and evaluation. The studies provide strong evidence that the spontaneous affect influences evaluative judgments through a more complex process, likely by coloring the interpretation of the fluency experience and the nature of resulting metacognitions relating fluency to liking. Theoretical and managerial implications of the findings are mentioned.