Since isolated ROCK1-deficient platelets exposed significantly more phosphatidylserine upon collagen activation, we tested the in vivo significance of this observation by measuring the tail-bleeding time, as well as the time for thrombus formation and occlusion in cremasteric venules in a light/dye-induced endothelial injury/thrombosis model. The gene discussed is ROCK1; the disease is Venous thrombosis.