Objective. The phenotypic complexity, together with the multifarious nature of the so-called ‘‘schizophrenic psychoses’’,limits our ability to form a simple and logical biologically based hypothesis for the disease group. Biological markers aredefined as biochemical, physiological or anatomical traits that are specific to particular conditions. An important aim ofbiomarker discovery is the detection of disease correlates that can be used as diagnostic tools. Method. A selective review ofthe WFSBP Task Force on Biological Markers in schizophrenia is provided from the central nervous system to phenotypes,functional brain systems, chromosomal loci with potential genetic markers to the peripheral systems. Results. A number ofbiological measures have been proposed to be correlated with schizophrenia. At present, not a single biological trait inschizophrenia is available which achieves sufficient specificity, selectivity and is based on causal pathology and predictivevalidity to be recommended as diagnostic marker. Conclusions. With the emergence of new technologies and rigorousphenotypic subclassification the identification of genetic bases and assessment of dynamic disease related alterations willhopefully come to a new stage in the complex field of psychiatric research.