The application of molecular genetics to the study of mental disorders has begun in earnest. Most of the initial interest has focused on the functional psychoses as these common and debilitating disorders have long been known to have a significant genetic component. A number of groups have now reported data from RFLP linkage studies of both schizophrenia and bipolar affective disorder (manic-depression). Unfortunately the results are already conflicting with early findings of linkage unconfirmed by subsequent studies.