Despite over a century of intensive research, no single biological marker has successfully translated into daily clinical practice. A key challenge in psychiatric research is that traditional diagnostic categories represent phenomenological constructs that do not necessarily circumscribe a biological homogenous entity, but encompass a whole range of disorders presenting with similar phenotypes. The clinical staging model shifts our focus to search for markers relevant to particular stages of mental disorders and provides a useful framework to differentiate overlapping and heterogeneous syndromes. The identification of such “stage” dependant markers may be more meaningful and of greater prognostic and therapeutic value than our quest for categorical disease markers. In this chapter, bioactive and inflammatory markers in emerging psychotic disorders are discussed. Their specific role in brain development, psychiatric disorder onset and management are reviewed. Implications for future research are also provided.