Spatial dynamics of fibrin clot formation in non-stirred system activated by glasssurface was studied as a function of FIX activity. Haemophilia B plasma was obtained fromuntreated patients with different levels of FIX deficiency and from severe haemophilia B patienttreated with FIX concentrate (Ahemphil B) during its clearance with half-life t1/2=12 hours. Asreported previously (Ataullakhanov et al. Biochim Biophys Acta 1998; 1425: 453-468), clotgrowth in space showed two distinct phases: activation and propagation. The activation phase ischaracterized by the time required to start clot growth from the activator, while the characteristicparameter of the propagation phase is the clot elongation rate. This rate reaches steady state inapproximately ten minutes after the beginning of growth. In haemophilia B plasma, clotformation is substantially impaired: clot starts to grow from the activating surface later than inhealthy donor plasma, and its propagation rate is considerably lower. The most significantabnormalities in clot growth kinetics are observed at FIX activity below 10% of normal.Simulation of these experiments was performed theoretically using a detailed biochemical model(Panteleev et al. Biophys J 2006; 90: 1489-1500) adapted for experimental conditions used.Suitability of the assumptions used to describe triggering contact activation was verified.