Aim: It is generally assumed that only unbound drugs can reach the site of action by diffusing across the membranes and exerting pharmacological effects by interacting with receptors. Recent research has shown that the percentage of free drugs may depend on the total drug concentration. The aim of the paper is to verify whether the mentioned dependence reported for propofol also takes place in plasma and human serum albumin samples in the presence of intralipid-the medium used as a vehicle for propofol infusions and a parenteral nutrition agent. Methods: Artificial plasma samples and human plasma were spiked with intralipid or ethanolic solutions of propofol. The samples were then assayed for free propofol concentration using ultrafiltration and high performance liquid chromatography with fluorimetric detection. Results: The decrease of the total drug concentration results in free propofol fraction increase, irrespectively of the used type of propofol solvent and sample type. The addition of intralipid causes the lowering of the overall free drug fraction with respect to the samples spiked with ethanolic solutions of the drug. Conclusion: The presence of intralipid does not influence the phenomenon of free propofol fraction rise at low total drug concentration. Such a rise cannot be ignored in clinical conditions when the drug is applied for sedative, antiemetic or other low-dosage purposes.