Suspiciousness of deception threatens the internal validity of the conformity experiment, and analyses suggest it is becoming more widespread. After being led to believe their own ability in a visual judgment task was higher, lower, or the same as the ability of the other group members, 65 undergraduate women made visual and informational judgments in the Crutchfield apparatus. Major findings include treatment effects on suspiciousness, less conformity by suspicious Ss, and ‘significant’ treatment effects on conformity only when suspicious Ss were removed from the analyses. Measures of self-confidence and confidence in others were significantly related to and likely determinants of suspiciousness. Implications for improving deception in conformity research are discussed.