The influence of warning signal timing and cognitive preparation on the aversiveness of electric shock. Many medical and dental procedures are noxious. Finding an optimal way of warning patients concerning the aversive procedures could help them to cope better. A model for the effective use of a warning signal in coping with pain posited that a person needs enough time to be able to react and should possess the skills necessary to utilize the time effectively. It was felt that a very short warning period, e.g., 5 sec, could not be long enough, while a 180 sec warning period would in and of itself become aversive. Reactions to electric shock were obtained from 36 paid, volunteer subjects who were each tested on a within-subject, counterbalanced order at 4 different warning periods: 5, 30, 60, and 180 sec. The subjects were divided into 3 groups: (1) the experimental group was provided with a pretested self-instructional booklet to learn a variety of pain control techniques; (2) the placebo group was provided with a self-instructional booklet on citizenship; (3) the control group waited quietly for 13 min. No significant results were obtained for the different pain-coping conditions. Significant differences, however, were obtained for the various warning periods. Maximum skin resistance changes, higher ratings of pain and of anxiety were obtained for the 60 and 180 compared to the 5 and 30 sec warning periods. Maximum heart rate was obtained for the 30 sec warning. Results were discussed in terms of the psychological meaning of the various measures as well as their clinical implications. 