A consistent finding in brand-alliance research is that a well-known, reputable brand ally improves consumers' evaluation of an unknown brand. The authors contribute to this research by examining the effects of a brand ally at different levels of cognitive elaboration and message argument strength. Results suggest that the brand ally serves as an endorser of the primary brand in two key ways. When cognitive elaboration is low and the ad contains strong arguments, the ally serves as an endorser. On the other hand, the presence of a reputable ally is an information cue when cognitive elaboration is high and the ad contains weak arguments. © 2006 Wiley Periodicals, Inc.