1. The capillary resistance test has been studied by a special technic of capillary microscopy.
2. Seventeen cases of hemorrhagic diseases of differing etiology have been thus studied.
3. The site of capillary hemorrhage has been localized to the arteriolar end of the capillary loop.
4. Selective damage to the arteriolar-capillary junction will explain many types of hemorrhagic syndromes.
ACKNOWLEDGMENT I wish to thank the honorary staff of the Westminster Hospital for permission to study cases under their care. I am much indebted to Dr. P. Hansell and Miss F. E. McAdoo of the Westminster Hospital Department of Medical Photography for assistance with the illustrations.