Microvessels of the nailfold were observed and photographed by capillary microscope in 144 patients with blood diseases. Their features and flow states were investigated with special reference to hematological findings. The results were followings: 1) Percent distributions of the patterns in the nailfold capillary loops were calculated. Hypoplastic anemia, iron deficiency anemia, chronic lymphocytic leukemia and idiopathic thrombocytopenic purpura (ITP) showed significant decrease of the open loops (by Gibson) and increase of the closed loops. These changes were most prominent in ITP. 2) Evaluation values of the morphological abnormalities were calculated in blood diseases. Acute myelocytic leukemia, chronic myelocytic leukemia, acute lymphocytic leukemia, chronic lymphocytic leukemia, hypoplastic anemia, iron deficiency anemia, allergic purpura and ITP showed significant high evaluation values compared with normal controls and ITP showed the highest among these. 3) No significant difference was observed between the number of the capillary loops per 1mm width in the nail fold of blood diseases and that of normal controls. 4) Significant narrowing in the diameter of the arterial and venous limbs was observed in acute myelocytic leukemia, acute lymphocytic leukemia, hypoplastic anemia and iron deficiency anemia. Polycythemia showed prominent dilatation of the limbs. 5) No significant correlation was observed between the red cell count of the peripheral blood and the number of the capillary loops. 6) Positive correlation was observed between the red cell count and the diameter of the capillary limbs. 7) Granular flow was significantly prominent in patients with accerelated erythrocyte sedimentation rate. 8) Granular flow in patients with white cell count of more than 50,000 was statistically more prominent than in patients with that of less than 50,000. 9) Granular flow in myelocytic leukemia patients was significantly more prominent than that in lymphocytic leukemias. 10) Significant correlation was observed between the granular flow and the apical dilatation of the capillary loops. 11) Capillary petechiae were observed in patients with blood diseases. 58.1% of 74 patients were positive. Bleedings were most frequent in "Schaltstuck" of the capillaries, and petechiae moved slowly to superficiallayer of the epidermis. 12) Capillary petechiae in the nailfold were significantly more frequent in female than in male but no correlation was observed between the cpillary petechiae and the following items, i.e. ages, Rumpel-Leede test, thrombocyte count, bleeding time and coagulation-fibrinolysis tests.