This in vitro study investigated time-related effects of propofol at the plasma concentrations required for sedation and general anaesthesia, on RBC aggregation, deformability, and morphology. Blood containing propofol at plasma concentrations of 0, 2 and 4 μg ml-1 was incubated in a water bath at 37°C for 1, 2, or 4 hours. RBC elongation indices (EIs) and aggregation indices (AIs), which represent RBC deformability and aggregation, respectively, were measured. Also, RBC morphological indices (MIs), which represent RBC morphology, were calculated. EIs and AIs were similar at propofol concentrations of 0, 2, or 4 μg ml-1 after 1, 2, or 4 hours of incubation. MIs at propofol plasma concentrations 0 or 2 μg ml-1 were similar after 1, 2, and 4 hours of incubation, however, MI at a propofol concentration of 4 μg ml-1 after 4 hours of incubation was higher than its value after 1 or 2 hours of incubation. No significant difference was observed between MIs at propofol plasma concentrations 0, 2, or 4 μg ml-1 after 1, 2, and 4 hours of incubation. At clinical doses, propofol has no direct effects on RBC deformability, aggregation, or morphology over a 4 hours incubation period.