Although a familial component to schizophrenia has been established through several family, twin and adoption studies, an inherited biological factor has yet to be established. Efforts to define clinical familial subtypes of schizophrenia have generally been unsuccessful, although recent data from our study population of pairs of siblings with schizophrenia suggests that schizophrenia with recurrent episodes of major depression may define one such group. There have only been a few biological traits consistently found to be associated with schizophrenia and also found to be heritable. These findings (e.g. measures of monoamine metabolism, brain structural morphology, neurophysiological markers, and protein polymorphisms) are reviewed in the present chapter. The proportion of patients with any of the noted abnormalities never approaches 100%, nor have any been found to be specific to schizophrenia. Research into the biogenetics of schizophrenia is clearly just beginning.