French and Raven (1959) proposed five bases of social power: referent, expert, legitimate, reward, and coercive power. Other power bases, such as information control and ecological control, have also been proposed. Another factor which might be considered a power base is the credibility of a source. A 2 x 3 factorial design was used to manipulate the level of power and the credibility of an actor. Vignettes were created in which a manager had either high or low reward and coercive power. The actor was described as having either high or low power, and was also described as having established high or low credibility in the past or no credibility information was provided. Vignettes were read by 84 undergraduate students who then responded to power scales and answered questions measuring credibility. The results revealed that the relationship between credibility and social power is a complex one. Credibility had no effect on power ratings in the high power condition, but in the lower power conditions the manager with high credibility was perceived as more powerful than the low credibility manager. Thus when the employee had low objective power, high credibility served to significantly enhance the power ratings for reward, coercive, referent, and legitimate power bases. (NB)