There have been many studies concerned with families of schizophrenics. Both environmental and genetic factors are claimed to be responsible in the development of this condition. Nowadays, there is no absolute hereditarian or environmentalist. A number of studies have shown that genetic factors are present in schizophrenia. The issue of whether this condition is caused by a single major gene with diminished penetrance or by polygenes has not yet been satisfactorily proven. Although this issue is difficult to resolve, it is important to distinguish between these two possibilities of genetic inheritance. In the case of single gene inheritance, biochemical investigation would be fruitful, but not in the case of polygenic inheritance manifesting clinical abnormalities once it exceeded a given margin of tolerance.