The role of expectations in OD has largely been ignored or treated as a methodological problem, yet available data indicate that OD may operate as a self-fulffilling prophecy. This article focuses on the hypothesis that expectations are a major force for changing organizational effectiveness. The author argues that the unintended raising of expectations for intervention outcomes may be a major causal variable. He hypothesizes that an OD intervention 's effectiveness is in direct proportion to the expectations for improved performance it arouses, and that attempts to control expectations for methodological purposes may hamstring the intervention. The author discusses consultants as prophets who may unwittingly fulfill their own prophecies and the Messiah effect, and concludes by suggesting that OD programs can and should deliberately raise expectationsfor improved productivity, which may be done with considerable practical gain and no loss of methodological rigor.