This is a report about a 14-year old girl who, following chemotherapy for malignant teratoma, developed a clinical state of SIADH (syndrome of inappropriate secretion of antidiuretic hormone). The causative agent was most likely vincristine (VCR). The important feature in this case was that the urinary kallikrein activity was high when she was affected by SIADH and decreased when her hyponatremia improved. Sodium clearance was significantly correlated with the increase in urinary kallikrein activity. It is considered that the kallikrein-kinin system may in part participate in the excessive natriuresis of SIADH.