An aversive stimulus with a signal elicits responses different from those for a stimulus without a signal. The characteristics of this phenomenon, called “signalling effect”, were clarified in this study. In Exp. I, the eyeblink reflex and 180°-rotation type of aversiveness rating were shown to be sensitive enough to study this effect. Three conditions which differed from each other in the ISI were used in a between-subjects design in Exp. II, and in a within-subjects design in Exp. III. The results of both experiments were as follows: The facilitatory signalling effects in the 8-s ISI condition and inhibitory ones in the .5-s ISI were found to be significant regardless of the index. Moreover, these effects had no learning factor.