Five investigations, involving SOI Ss and SI £s, were conducted to crossvalidate an earlier study (Rosenthal & Fode, 1963, Exp. 1) that bad clearly demonstrated the Experimenter Bias Effect. Each of the five investigations failed to demonstrate that £s' expectancy-biases influence their results (overall F<1.0). The five investigations are related to other studies in this area, the majority of which also failed to demonstrate the Experimenter Bias Effect. It is concluded that the effect is more difficult to demonstrate than was implied in several recent reviews and that, at the present time, it is not known what preconditions are necessary to obtain it.A recent text (Rosenthal, 1966) delineated several ways that an experimenter might inadvertently influence the results of his research. These "experimenter effects" include an Experimenter Personal-Attributes Effect in which the characteristics or personality traits of the experimenter-for example, his sex, age, race, anxiety, need for approval, hostility, and dominance-influence his 5s' performance. They also include an Experimenter Bias Effect in which E's expectancies, hypotheses, desires, or biases affect the results. For instance, an Experimenter Bias Effect would be present if Es obtain significantly higher scores from 5s on a standard test when they expect high rather than low scores.This paper is concerned only with the Experimenter Bias Effect. There is little doubt that Es generally expect or desire to obtain different results from 5s assigned to different 1 These investigations were supported by research grants (MH-07003 and MH-I1S21

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