Ecological studies on the distribution of rates of first-admitted schizophrenics were carried out in Mannheim in 1965 and from 1974 to 1980. As the catchment area of the ABC Schizophrenia Study comprises the cities of Mannheim and Heidelberg, we were able to conduct a third ecological study for Mannheim and a first study for Heidelberg covering the years 1987 to 1989. High rates of schizophrenic residents are found in the inner districts of Mannheim and Heidelberg. This concentration has been stable over a period of 25 years for Mannheim. Subdividing the districts of Mannheim and Heidelberg into zones, only in Heidelberg and only for the second cross-section in Mannheim, the rates decreased constantly with increasing distance from the centre. Summing up the districts of Mannheim and Heidelberg in homogenous areas on the basis of economical and socio-demographic properties, high rates of schizophrenics were found in homogenous areas with poor and unfavourable living conditions. In Mannheim and Heidelberg, homogenous areas with the highest rates of schizophrenics are characterised by highly unfavourable living conditions, a high percentage of young men, people living alone, students, foreigners, people with a low level of education and a high immigration/emigration rate. The analysis on the individual level, i.e. in the biography of schizophrenics shows that processes of social drift and/or nonstarter take place long before first admission in the prodromal phase and the psychotic prephase of beginning schizophrenia. Probably, these selective processes like downward drift or nonstarting processes, lead to the migration of schizophrenics into unfavourable areas or schizophrenic residents staying in poor areas, while healthy residents leave these districts. Selective processes such as help seeking behaviour and access to the care system have no effect on the unequal distribution. In summary, a definite confirmation or refutation of one of the two causal hypotheses, 'social selection' vs. 'social causation', is not possible up to date, but the empirical results support the selective hypothesis for schizophrenic disorders.