Could many forms of mental illness be manifestations of spiritual possession? Is the ancient rite of exorcism an effective instrument for healing certain forms of ""insanity""? These questions are investigated by the prolific author (Mind Beyond the Body, 1978; Miracles, 1981, and some 17 others), who is currently a lecturer on parapsychology at California's John F. Kennedy Univ. Unfortunately, the answers he comes up with are, like his oxymoronic title, ambiguous. In tracing the history of modern possession, Rogo rehearses in detail the careers of such well-known delvers into the paranormal as James H. Hyslop, Dr. Titus Bell, and the currently best-selling author/psychiatrist M. Scott Peck. He attempts to show how several of their patients have exhibited signs of possession, multiple personalities, and out-of-body experiences and, more importantly, how these aberrations may be caused by discarnate spirits. Readers will probably find Rogo far too willing to accept the claims of these parapsychologists and too lackadaisical in probing into alternative (and less sensational) explanations for their findings. The author, for example, seems reluctant to ascribe fraudulence to the mediums employed by these investigators. When he does mention accusations of fraud, these matters are generally dismissed with a sweeping ""most of the specific charges turn out to be baseless."" Further explanations are called for--why ""most""? how ""baseless""? All in all, a smoothly written overview that promises more than its author seems able to produce.