A method of preparing a blood platelet lysate starting from platelet-rich plasma from whole blood of animals, to which blood a citrate has been added to prevent coagulation, is described. The method is characterised by concentrating the platelet-rich plasma by ultrafiltration to obtain a plasma that is richer in platelets, adding water for lysis of the platelets included, adding Ca.sup.2+ to the lysed concentrated platelet-rich plasma for forming coagel of other components than lysed platelets, centrifuging the coagel, whereby a clear, bright-red liquid of blood platelet lysate is obtained, which substantially consists of lysed platelets, and a coagulate, and, after centrifugation, the liquid going through a filtering step.