SummaryThe factors that serve to maintain a normal vascular resistance are largely unknown. Yet, pathological vascular fragility may be semi-quantitatively determined by the tourniquet-test or the suction-cup test. These tests even allow to draw certain conclusions concerning the pathogenesis of the hemorrhagic disorder. Nevertheless the clinician must be aware of their limitations and submit the results to a critical evaluation, especially because of their variability.Tissue biopsy is extremely useful for the making of a diagnosis, in the hemorrhagic conditions where there is neither coagulation defect nor platelets anomalies.