While he was attending Washington's Georgetown University in 1949, William Peter Blatty read about the reported exorcism of a 14-year-old boy in nearby Mt. Rainier, Maryland. The entire subject of diabolical possession came to fascinate Blatty, and two decades later he wrote a novel on the subject that proved equally fascinating to millions of readers. Since its publication in 1971, "The Exorcist" has sold over 6,000,000 copies in the United States alone, and has been translated into 18 languages and has reawakened world-wide interest in the whole spectrum of supernatural phenomena. The Maryland case on which Blatty modeled his tale about a possessed young girl was by no means the only such incident in recent times. Exorcistic ceremonies remain a bastion of certain Eastern cultures, several Western exorcisms in this century have been extensively documented and countless others have undoubtedly been performed in the secrecy still enshrouding this ancient practice. Ours is a skeptical age, and a host of physiological and psychological explanations have recently been advanced for cases of "diabolical possession." Psychosurgery, arteriography and newly discovered drugs are all scientific alternatives to the ritual of exorcism. Yet no discovery has enabled us to understand the fundamental nature of evil and its irrational, violent, persistent infestation of man throughout history. By charting the specific symptoms of a young girl presumed "possessed" and detailing the methods by which the demon was exorcised from her, Blatty hoped to frame the unending battle between good and evil in a dramatically compelling and philosophically provocative narrative. Director William Friedkin's film version of "The Exorcist," which opened in 1974, has the same goal; to look realistically at the inexplicable events during a thoroughly documented, bizarre outbreak of evil in one contemporary American home.