This is the second in a series of articles on the role of the experimenter and additional personnel (other than the subject) taking part in parapsychological experiments. It reviews the evidence for psi-mediated experimenter effects, or the communication of experimenter bias, when all normal (i.e., sense-based) channels of communication are eliminated. Experiments in two broad categories are reviewed: (a) nonintentional psi experiments in which the subjects are unaware of certain important aspects of the test situation, or may not even know that they are taking part in a psi test; and (b) experiments in which the experimenter deliberately tries to influence the results by means of his own PK or ESP. When significant results are obtained in the first category, they may be due either to telepathy from the experimenter and/or his associates (psi-mediated experimenter effects) or to clairvoyance of the testing situation on the part of the subject (psi-mediated experimental effects). Significant results in the second category suggest either a direct influence of the experimenter upon the subject's responses by means of PK or an indirect influence by means of ESP. It is concluded that in psi research it may not be possible to differentiate between the experimenter and his experiment, and, therefore, between psi-mediated experimenter and psi-mediated experimental effects.