It is argued that a diathesis-stress theory, in which an attempt is made to identify genetic and environmental factors and their interaction, is the most hopeful framework for construing the etiology of schizophrenia. Pairwise concordance rates in the Maudsley schizophrenic twin study, based on the consensus of six diagnosticians, were 50% for MZ and 9% for DZ pairs. Environmental factors were believed to be nonspecific and genetic factors specific. Findings in the literature and our own study were consistent with polygenic inheritance. Assuming schizophrenia to be a threshold character, independent estimates from various classes of relatives showed heritability of the underlying liability to the disorder to be high and were in substantial agreement. This was particularly so when the population incidence was taken to be 1 %. It is argued that some genes may have a much larger effect than others in accounting for trait variance, and that these may be found to influence specific facets of the syndrome. Our model involves interaction with the environment in a complex network of events at all stages, including symptom amelioration, and it is seen as bridging the gap between geneticism and environmentaiism.