Quantitatively accurate measurements of plasma free fatty acid (FFA) turnover can be made if the FFA tracer is infused intravenously and arterial blood is sampled. To be certain that arterialized-venous blood provides comparable information, plasma FFA concentration and specific activity were measured in both arterial and arterialized-venous blood in 19 volunteers undergoing infusion of [1-¹⁴C]palmitate infusion before and during a euglycemic, hyperinsulinemic clamp. Heated hand vein blood was obtained using either the heated box (n = 9 subjects) or heating pad (n = 10 subjects) technique. The heated box arterialized-venous blood had palmitate concentration and specific activity equal to arterial blood. The use of the heating pad resulted in small (3%), but statistically significant (P < .05), underestimates of palmitate specific activity. In addition, plasma lactate concentrations were significantly higher in heated hand vein blood than arterial blood. In summary, heated hand vein blood is a satisfactory alternative to arterial blood for tracer studies of FFA metabolism.