The identification of genes that contribute to the susceptibilities to complex neuropsychiatric disorders such as schizophrenia, major depression and bipolar disorders has not been as successful using conventional genetic approaches as had been hoped. There are several problems associated with the conventional approaches, including the validity of psychiatric diagnosis itself, excluding carriers of relevant genes who cannot be identified in the absence of manifest symptoms, and the heterogeneity of neuropsychiatric disorders, both clinically and etiologically. A new direction that appears encouraging is the identification of neurobiological and neurobehavioural characteristics, hidden from the "naked eye" associated with these complex neuropsychiatric disorders. These characteristics are termed endophenotypes, that may be more closely linked to gene expression in the causal chain from genes to psychiatric diagnosis disorders [1,2]. An endophenotype is a special kind of biomarker, one that is not the consequence of illness and is heritable. It plays an important role for bridging the gap between the microscopic level (e.g., molecular genetics) and the macroscopic level (e.g., clinical symptoms) of neuropsychiatric disorders such as schizophrenia and bipolar disorders [3,4]. The identification of endophenotypes is very crucial to the identification of genes that predispose someone to neuropsychiatric disorders. Therefore, the study of endophenotype is of particular usefulness for us to understand the underlying mechanism of the illness process of neuropsychiatric disorders, aiding the clinicians to make accurate diagnosis and for early detection purposes. The Director of the United States National Institute of Mental Health (NIMH), Thomas R. Insel and his associate Dr. Bruce N. Cuthbert have provided an ideal overview of the importance of endophenotypes in the context of the mission of the NIMH [5] and have provided pointers [6] to exciting developments in revising diagnostic practices that utilize endophenotypes.A substantial number of studies, especially of at-risk off-spring of patients, have suggested that neurocognitive dysfunctions are among the most promising of the candidate endophenotypes. With the completion of the human genome project, the main hurdle for scientists working with neuropsychiatric disorders for the next decade will be how to characterize the manifold human endophenotypes from the molecular level to the mind level, and most importantly, detecting unharmonious heritable contributors to the mind in neuropsychiatric disorders. The development of cognitive neurosciences, neuropsychology and imaging genetics-a strategy for mapping neural structures and brain activity as a function of genotype in living humans -has encouraged a conceptual transformation by showing that the greater power of endophenotypes lies in using genetic risk variants as tools for discovery of the mediating neural mechanisms that bridge the gap from DNA sequence to pathological behaviour.