Cultivation of Staphylococcus aureus in a fermenter significantly improved production of coagulase (Fig. 1,2,3). Optimal coagulase-activity was reached in the culture supernatant after inoculation with 8 x 10(9) colony-forming S. aureus per ml of brain heart infusion broth and 20 min at 37 degrees C. At this time most of the other enzymes and toxins (particularly protease and staphylokinase) had not been formed or only in small amounts. Characterization of coagulases from respectively 5 S. aureus-cultures from humans, cattle and dogs revealed molecular weights between 56800 and 71000, and isoelectric points between 5.4 and 6.4 (table 1).