While there are some inconsistent reports whether S100B levels decline with treatment response (Schroeter et al., 2002) or not (Hetzel et al., 2005; Jang et al., 2008; Schroeter et al., 2008), the present study strongly suggests that S100B rather is a trait marker for antidepressant responsiveness than a state marker for depression severity. This evidence concerns the gene S100B and depressive symptom measurement.