Subliminal stimulation is defined as that which is perceived by an individual below the threshold of awareness or cognizance. This article traces the history of research in subliminal stimulation to illustrate that under certain circumstances and conditions, this behavioral phenomenon does occur. Although subliminal stimuli do affect human response, the article asserts that there is no sound evidence available to prove its effectiveness in changing behavior. Rather, studies show that the subject's motivational state determines the effectiveness of the stimuli; people do not act contrary to their desires. The article concludes with observations regarding the ethics involved in using this type of communication. (MAI)