Hepatocyte growth factor (HGF) is a pleiotropic cytokine known to be involved in tissue regeneration and repair. We measured serum levels of HGF in patients with insulin-dependent diabetes mellitus (type 1). The patients were divided into four groups: (1) 10 patients at clinical presentation before insulin treatment; (2) 19 patients with newly diagnosed type 1 diabetes (diabetes duration 1/2-3 years); (3) 14 patients with long-standing type 1 diabetes without renal involvement (diabetes duration >10 years, and urinary albumin excretion (UAER) <20 microg/ min); and (4) 20 patients with long-standing type I diabetes with renal involvement (diabetes duration >10 years and UAER 20-500 microg/min). Sera from 24 age- and sex-matched healthy blood donors constituted a control group. The HGF levels of the four groups were (mean +/- SD); group 1, 0.74+/-0.14; group 2, 0.78+/-0.40; group 3, 0.86+/-0.42; group 4, 0.79+/-0.27 ng/ml, compared to 0.43+/-0.24 ng/ml in the control group (P<0.0008). HGF levels were not significantly different between the four patient groups. The elevated serum HGF levels did not correlate with complications related to type 1 diabetes, such as UAER, retinopathy and macrovascular complications, suggesting that HGF levels were not associated with the type 1 diabetes complications. In conclusion, our results show that type 1 diabetic patients have increased serum HGF levels compared with controls and that HGF is elevated to the same extent in newly diagnosed as well as in long-standing type 1 diabetes.