Proposes an explicit definition of consumers' product expectations as pretrial beliefs about the product. Specific expectations about a product characteristic were created by exposing 38 married female consumers to 3 advertisements, each of which described 1 salient attribute of the product (ground coffee). These expectations were then negatively disconfirmed by a controlled trial experience with the product. For a wide range of cognitive variables, the disconfirmation caused negative changes in product evaluations. However, postdisconfirmation evaluations were not so negative as the product ratings of a nondisconfirmed control group that merely evaluated the product in absence of manipulated expectations. Results are consistent with both dissonance and assimilation-contrast theory. (30 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1979 American Psychological Association.