The invention relates to a method for determining the coagulation time of a sample fluid containing blood components by means of a resonator whose vibration parameters are measured and then used as a basis for determining the sample fluid viscosity change, which resonator has an at least partially adhesive surface contacting said sample fluid. The invention is characterized by preincubation of said surface with a preincubation fluid containing blood components, which preincubation fluid has a known way of interacting with the coagulation system, thus resulting in anchoring sites to be formed on the adhesive areas of said surface.
