The primary role of a decision support system is to guide and support a decision maker. As reliance on a decision support system is largely discretionary the persuasiveness of the system becomes critically important. In this paper characteristics thought to affect systems persuasiveness are examined. This paper asserts that the target and source of a decision support message, along with the design of the message itself, act to influence the persuasiveness of the decision support provided. Using a purpose built experimental platform with seventy subjects the research finds that the persuasiveness of a decision support message is varied by the perceived difficulty of the task being undertaken, and the perceived usefulness of the decision support provided. The type of decisional guidance provided also affects persuasiveness of the system; in particular, providing suggestive decisional guidance is shown to significantly improve system persuasiveness. The implications of these findings relate to the appropriate design of decision support systems, and the contexts within which a decision support system can be expected to persuade decision makers to reply on the support provided.