Aims/hypothesis: Insulin increases plasma non-esterified fatty acid (NEFA) clearance in humans, but whether this is independent of change in plasma NEFA appearance is currently unknown. Methods: Nine non-diabetic men (aged 28 ± 3, BMI 27.2 ± 1.7 kg/m²) underwent euglycemic clamps to maintain low (LINS) vs. high physiological insulin levels (HINS) for 6 hours. An intravenous infusion of heparin and Intralipid (HI) was performed during 4 of the 6 hours of the clamps (in the last 4 hours at low and in the first 4 hours at high insulin level) whereas saline infusion was administered in the remaining 2 hours to modulate plasma NEFA levels independent of plasma insulin levels. Four experimental conditions were obtained in each individual: LINS with saline (LINS/SAL) and with HI infusion (LINS/HI), and HINS with saline (HINS/SAL) and with HI infusion (HINS/HI). Results: Plasma palmitate appearance during HINS/SAL was lower than during the three other experimental conditions (P < 0.05). In contrast, plasma linoleate appearance, as expected, was increased by HI independent of insulin level (P < 0.02). Plasma palmitate clearance during HINS/SAL was higher than LINS/SAL and LINS/HI (P < 0.008) and this increase was blunted during HINS/HI. We observed a linear decrease in plasma palmitate clearance with increasing plasma NEFA appearance independent of insulin levels. Plasma NEFA levels increased exponentially with increase in plasma NEFA appearance. Conclusions: Insulin stimulates plasma NEFA clearance by reducing endogenous appearance rate of NEFA. The relationship between plasma NEFA level and appearance rate is non linear.