Human platelets take up and metabolize long-chain free fatty acids (FFA). Experiments in which platelets were loaded with 14C-palmitate, homogenized, and then fractionated indicated large amounts of membrane-bound FFA. In other studies, platelet membrane fractions took up FFA from incubation media containing albumin-bound FFA. These findings suggested that a large portion of the platelet FFA uptake might be associated with the platelet surface. Radioautography with electron microscopy using 3H-palmitate-labeled platelets provided additional evidence that much of the newly incorporated FFA was associated with the platelet surface.