Midkine (MK) is a heparin-binding growth factor, which promotes growth, migration, and survival of various cells, and MK expression is increased in many human carcinomas. We determined the urinary MK level by enzyme-linked immunoassay. Taking 311 pg/mg creatinine as a cut-off level, 70% of patients with various carcinomas (n = 142) gave positive values, while only 5.5% of healthy volunteers (n = 330) did. In case of gastric carcinoma, 17 out of 21 patients with stage I tumor were positive. Urinary MK levels are expected to become a convenient marker as an aid in detection of tumors. (C) 2003 Elsevier Science (USA). All rights reserved.