Some individuals claim to have come into contact and communicated with occupants of flying objects of extraterrestrial origin who often would have entrusted them with "missions" regarding the safeguard of humanity. The authors, who have observed six such subjects, conclude that five of them suffered from a paranoid delusional state often akin to paraphrenia; whereas other analogous cases previously reported have been diagnosed as suffering from paranoid schizophrenia. Their beliefs, inaccessible to criticism and to reasoning, presumably help them to remain outside psychiatric reach. The present article does not take an interest in the physical existence of this phenomenon and does not wish to be reductionistic. It does not claim to express a judgment on the witnesses of such phenomena whose mental health must be evaluated through a rigorous and impartial examination, and not be evaluated in terms of the examiner's preconceptions toward the witnesses' assertions.