Besides the lowering of blood pressure, there were several hematological changes during the anti-platelet serum shock in dogs, which can be summarized as follows: striking hemodilution, disappearance of platelets, low leukocyte values, tendency to low sedimentation rate, maintenance of specific gravity of plasma within the normal range, elevation of coagulation time, and a few cases where incoagulability was observed. This hematological picture is reversible, when the animal recovers from shock, except for the platelets which never appear again in the circulating blood.