This paper presented the cumulative knowledge that the authors gained about the "sleeper effect" during a series of 5 experiments. The "sleeper effect" is the improved effects of communication over time -- after one has a chance to "sleep on it." From their experiments, the authors conclude that, at best, the "sleeper effect" is statistically an unreliable phenomenon. In addition, when presented with truism-opposing communication, relayed in short paragraph segments, subjects' reactions indicated that the low-credible source induced substantially more discounting (but not more counterarguing) than did the high-credible source. Also, the prior counterargument defense induced substantially more counterarguing (but not more discounting) than did the no-defense condition. A plausible hypothesis was revised to read: audiences may be more susceptible to the effects of a similar communication from a new source when their response to an initial communication has been discounting rather than counterarguing. (TA)