Starting from the 722 probands originally studied by Rüdin, Bruno Schulz re-examined them and their relatives confirming the diagnosis in 660. While Rüdin sought for mendelian ratios in siblings, Schulz, anticipating modern methods, focused on the family study method as an approach to clarifying possible etiologic heterogeneity within the schizophrenia syndrome. Using a Kraepelian approach to diagnosis, Schulz reports a MR for narrowly and broadly defined schizophrenia of 6.7 and 8.2% in siblings and 2.6 and 3.7% in parents. He found no evidence for a difference in risk of illness in siblings as a function of either the gender or outcome of the proband. The risk for schizophrenia was significantly increased in siblings of hebephrenic probands. Compared to siblings of probands with no identified factor which precipitated their schizophrenia, the risk for schizophrenia was significantly decreased in probands with a physical etiologic factor but did not differ in siblings of probands with a psychological etiologic factor. The risk for schizophrenia was particularly low in siblings of probands whose onset of illness occurred within a year of major head trauma.