Polylactic acid nanocapsules of clofibride containing soybean oil (SO) or medium-chain triglycerides (MCT) as the oil core were prepared. The in-vitro drug release kinetic profiles were determined and compared to those of a clofibride submicron emulsion using two different kinetic techniques: the bulk equilibrium reverse dialysis sac technique, and the centrifugal ultrafiltration technique. The former technique was shown to be inadequate for in-vitro kinetic comparison purposes as a result of drug diffusion limitations through the dialysis membrane. The latter technique yielded rapid in-vitro release profiles of clofibride from both emulsion and nanocapsule delivery systems under perfect sink conditions although a consistent lower maximum drug amount was released from the MCT nanocapsules as compared to the corresponding emulsion. This was attributed to the relatively higher aqueous solubility of MCT as compared to SO. This comparative study, carried out, to the best of our knowledge, for the first time, clearly showed that both colloidal carriers behave similarly with respect to drug release despite their different morphological characteristics. The kinetic results dearly exclude either the use of submicron emulsion or of nanocapsules as colloidal controlled release delivery systems for any administration route where perfect sink conditions should prevail.