Intravenous injection of histamine phosphate in the dog in a dosage of 50-200 μg/kg body weight increased the fibrinolytic activity of the plasma and of the euglobulin fraction of the plasma. The plasma antiplasmin and protein content of the euglobulin fraction were not altered. The level of GOT in the plasma increased after injection of histamine but the rise appeared later than the rise in fibrinolytic activity.