A preliminary but growing body of evidence supports the existence of biological substrates in personality disorders. Based on a review of the literature, the article deals with the major biological markers: genetic, cognitive, biochemical, electrophysiological and organic markers, of schizotypal and borderline personality disorders. In addition, the article compares these findings in these two types of pathological personality. In the field of genetics, we notice several indices in favour of a relationship between schizotypal personality disorder (SPD) and chronic schizophrenia. In contrast, in borderline personality disorder (BPD), indices were lacking for such a relationship between this disorder and one of the axis I diagnosis, or a clear genetic transmission. In the field of cognitive tests, we can note in both SPD and BPD, that the abnormalities which would be at the level of temporal and frontal lobes, may be implicated in the observable cognitive troubles in these two disorders. In the field of neurobiochemistry, the dopaminergic and serotonergic systems seem to be implicated in the etiology of SPD while several data point out the fact that several neurotransmitter systems (dopaminergic, serotonergic, noradrenergic and cholinergic) seem to be involved in the etiology of BPD. Finally, in the field of electrophysiology, we notice that some of these tests observed in SPD (smooth pursuit eye movements, evoked potentials, modification of the electrodermic response) seem reinforcing the relationship between SPD and schizophrenia while those observed in BPD seem reinforcing either a relationship between BPD and depression (sleep studies), or a relationship between BPD and schizophrenia (evoked potentials, smooth pursuit eye movements).