The invention provides a method for determining platelet function in a mammal comprising providing platelets from the mammal, contacting the platelets in suspension with at least one immobilised ECM protein or an effective fragment or analog thereof while applying to the platelets an effective mechanical stimulus for an effective period of time and determining the platelet activation produced. The invention also provides a method for detecting a bleeding disorder in a human. Further, the invention provides a method for monitoring the efficacy of pharmacological agents affecting platelet function in vivo.