Inactive kallikrein (prekallikrein) in human urine was discovered recently. A more accurate method to measure this zymogen and total kallikrein is described. With trypsin pretreatment, it was found that 35.3 +/- 2.7% of total urinary kallikrein activity was prekallikrein. The results are supported by a new direct radioimmunoassay which measures predominantly active kallikrein.
