Non-esterified fatty acids (NEFA) play a complex role in glucidic homeostasis. This role led us to investigate their quantification in diabetic patients. The plasmatic NEFA concentrations, measured with the FA115 kit of Randox, showed significant differences between control patients (0.42 +/- 0.14 mmol/L, N = 50) and diabetic patients (0.68 +/- 0.35 mmol/L, p < 0.01, 443 diabetic patients (70 with type l and 373 with type 2 diabetes)). NEFA concentrations were significantly higher in type 2 diabetics (0.70 +/- 0.32 mmol/L) when compared to type 1 diabetics (0.59 +/- 0.35 mmol/L, p < 0.05). In type 2 diabetics, a significant correlation was observed between NEFA and glucose concentrations at 8 hrs a.m., and the mean glucose concentrations along the day (p < 0.001). In contrast NEFA concentrations were less correlated to levels of HbA1c. NEFA were well correlated with cholesterol and triglycerides (p < 0.05) but not with Lp(a). They were also correlated with BMI but not with age or duration of the disease. Diabetic patients on metformin associated to lipolytic treatment, presented lower concentrations of NEFA and better glucidic control. The results confirm the role of NEFA in glucidic homeostasis and suggest an interest for their routine determination.