The c-met proto-oncogene encodes the receptor to hepatocyte growth factor-scatter factor (HGF-SF), a mesenchyme-derived cytokine with cell-dissociating, invasion, and angiogenic properties. The expression of c-met in breast cancer is the subject of controversy; 111 primary breast cancers were examined for LOH of c-met by Southern blot electrophoresis. c-met expression was measured in a further 40 patients with breast cancer and in 8 patients with benign breast disease by flow cytometry. LOH of c-met was detected in only 4% of informative breast cancers. Expression of c-met was significantly greater in patients with breast cancer than in those with benign breast disease (P <0.01, Mann-Whitney). There was no correlation however between increased c-met expression and clinicopatho-logical prognostic variables. These results do not support the role of c-met as a tumour suppressor gene in breast cancer but suggest increased receptor expression in malignant breast disease. The significance of this increased expression in breast cancer is the subject of further investigation. © 1995 Wiley-Liss, Inc.