The effects of varying knowledge of an information system and belief in the effects of this information on discomfort during dental treatment were measured. The information system consisted of patient-operated buttons connected to a series of lights which provided continuous information to the dentist concerning the relative comfort of the patient. Actual information, false information, and knowledge of the information system were combined to form experimental groups. The results showed that those individuals with the ability to provide information to the dentist reported less discomfort than those without this ability during a scaling procedure. During the polishing procedure, the belief of the effect of information resulted in a decrease of reported discomfort.