Advances in genetic mapping of human diseases have led to the identification of single locus susceptibility for several common disorders. There have been a number of reports of linkage for the psychiatric disorders manic-depressive illness and schizophrenia, but none of these linkage reports is uncontested. Nonetheless, it appears promising to continue attempts to map these psychiatric disorders, since linkage can now be detected even when the inheritance is complex and includes genetic heterogeneity and variable penetrance.