In the paper, a microtiter plate method was used to determine the residual prekallikrein activator(PKA) activity in blood products.The result of study indicated that it would be satisfactory that the reaction mixture of PKA and prekallikrein (PK) was iucul ?? at room temperature for 30 minutes with 0.05M Tris/0.15M NaCl buffer(pH 8.0) , and then the mixture continued to be incubated at room temperature for another 15 minutes after the chromogenic substrate for kallikrein was added. The method had a good reproducibility. The PKA contents determined in IVIG agreed with that of the processing method of IVIG and the hypotensive test of rats, and were basically consistent with the result, determined by the method developed by the Finnish Red Cross Blood Transfusion Service.