OBJECTIVE The aim of this study was to investigate circulating soluble Fas (sFas) and Fas ligand (sFasL), two transmembrane glycoproteins involved in apoptosis, in the serum of diabetic patients. MATERIAL AND METHODS We assessed sFas and sFasL serum levels in normal controls (n=15), and in both 42 diabetic patients without complications, or with predominant retinopathy or neuropathy, using sFas and sFasL specific ELISA method. RESULTS sFasL serum levels were less than 0.1 ng/ml in normal controls and in each group of diabetic patients. In diabetic patients with a predominant neuropathy, sFas serum levels were significantly increased not only when compared with normal controls (13.5 +/- 3.6 ng/ml vs 7.1 +/- 1.1 ng/ml, p<0.001), but also when compared with patients without complications (vs 9.1 +/- 1.8 ng/ml, p<0.001) or with a predominant retinopathy (vs 8.7 +/- 1.9 ng/ml, p<0.001). CONCLUSIONS These preliminary data suggest that a dysregulation of the Fas system in peripheral neuronal cells may be involved in the increase of sFas observed in diabetic patients with neuropathy.