As part of the introduction to an experiment using the Harvard Group Scale, subjects were given one of three brief instructions before being hypnotized: (1) no mention of negative or positive aftereffects, (2) vague warning of negative aftereffects, i.e., "some mildly unpleasant experiences", plus, "most persons report their experiences to be pleasurable and interesting", (3) specific warning of negative aftereffects, i.e., "approximately one half subjects have reported mild, short-term aftereffects such as headache", etc. (no positive information). The "specifically warned" Ss showed more negative aftereffects than both of the other groups, and the "no mention" Ss showed more than the "vaguely warned" Ss. The positive suggestions in the "vaguely warned" Ss instructions may have confounded the expectation for negative effects. A follow up study used instructions varying only in the degree of expectations for negative aftereffects (no mention of positive aftereffects). The results did not show group differences in negative aftereffects as predicted, however, correlational results suggested some interesting interactions among subject variables and the type of prehypnotic instructions administered.