To limit the genetic heterogeneity of schizophrenia, this study focused on the widely extended pedigrees of Ashkenazi Jewish schizophrenia probands. The hypothesis posed is that the increased prevalence among the Ashkenazim of the rare lysosomal enzyme disorders, Tay Sachs disease (TDS), caused by low levels of hexosaminidase A, and Gaucher's disease (GD), caused by low levels of glucocerebrosidase, might contribute to the demonstrated increased vulnerability to schizophrenia in this ethnic group. Signs and symptoms characterizing the candidate illnesses were systematically queried by the family history method. Rates and relative risks for symptoms characterizing these disorders and for several nonautosomal illnesses associated with TSD and/or GD (i.e., amyotrophic lateral sclerosis and Hodgkin's disease, leukemia and lymphoma) are significantly elevated in the schizophrenia pedigrees, compared to controls. The conditions with elevated rates and risks have been associated with chromosomal regions 1q21 and 15q23-q24. These areas are suggested as candidate regions for future targeted deoxyribonucleic acid (DNA) research in schizophrenia.