We examined the association between an elevated plasma TGF-beta 1 level and the disease progression of advanced breast cancer (BC) patients (n = 44). TGF-beta 1 levels were detected by an enzyme-linked immunosorbent assay (ELISA). Platelet carryover and in vitro platelet activation in our plasma samples was assessed and found to be insignificant. Plasma TGF-beta 1 values were significantly elevated (P < 0.05) in stage IIIB/IV patients (median value: 2.40 ng/ml, range: 0.13-8.48 ng/ml, n = 44) compared with healthy donors (median value: 1.30 ng/ml, range: 0.41-4.93 ng/ml, n = 36). Although pronounced in metastatic patients, especially those who had been newly diagnosed, TGF-beta 1 elevation was independent of tumour mass, site of distant metastases, histopathological type, steroid receptor (SR) content and age of the BC patients. Follow-up of 6 patients indicated a relationship between the plasma TGF-beta 1 and the patient's response. This suggests that TGF-beta 1, may be a promising prognostic marker for breast cancer patients with advanced disease. Confirmatory large-scale studies are needed, particularly given the overlap of values between our different subgroups analysed.