A primary concern in the psychology of religion is the distinct possibility that responses to empirical assessments of individuals' degree and type of religiosity and spirituality are exaggerated owing to social desirability bias. In spite of increased secularization in American culture and a growing distrust of organized religion, religious involvement, personal religiosity, and spirituality are still viewed as highly desirable characteristics. This study estimates the extent of social desirability biases that affect self-reports of religion and spirituality by utilizing a bogus pipeline procedure. In this procedure, participants are convinced that experimenters can detect disingenuous responses to individual items on questionnaires through the use of physiological measures, although no physiological data are actually collected. If the self-reports of participants in the bogus pipeline condition indicate greater religiosity or spirituality than those in the control condition, self-report bias is indicated. The bogus pipeline procedure has been used in other areas of study to increase veracity of self-reports when social desirability effects are present (such as reporting sexual behaviors or prejudice). The results indicate that social desirability biases influence multiple constructs including religious orientations, religious coping, and daily spiritual experiences. Implications for future research relying on self-reports of religion and spirituality are discussed.