OBJECTIVE To investigate the protein C-activating property and experimental conditions that may affect the activities of protein C activator (PCA-SV). METHODS PCA-SV's functional characteristic, possible anticoagulant and amidase activities were measured by method of APTT and that of specific chromogenic substrate respectively in various experimental conditions. RESULTS PCA-SV can specifically act on protein C. The pH-optimum and temperature-optimum for the action of PCA-SV were 6.0 - 7.0 and 37 - 40 degrees C respectively. The anticoagulants (heparin, sodium citrate) had no effect on the activities. CONCLUSION PCA-SV is a new protein C-activating reagent that has high potency and specificity.