A central theme in 18th-century Protestant theology is the pious subject. This is reflected in the many edifying writings and prints on self-examination and introspection. This article begins with an introduction to the theological understandings and developments that underlie the practice of soul diagnosis. The article then shows how the "inner person" becomes an object to be observed with empirical records and then analyzed to aid in salvation or healing. At the same time, we find an increased demand for (self-)examination and attention to one's health, understood as the unity of soul and body. New classification systems and diagnoses emerge that are widely disseminated and have reached far beyond their religious origins.