A possible protective effect of propionyl-L-carnitine on human endothelial cells was studied both under basal culture conditions and in the presence of agents capable of influencing oxidative damage, such as glucose/glucose oxidase and oxidized low-density lipoproteins. Propionyl-L-carnitine had no significant effect on the observed decline in various parameters of cell viability, e.g., cell detachment, release of lactate dehydrogenase, and the rate of protein synthesis. Propionyl-L-carnitine progressively decreased the fluorescence intensity in fura-2-loaded endothelial cells obtained during excitation at 340 nm. A similar effect was observed with propionyl-L-carnitine and acetyl-L-carnitine, but not with L-carnitine and D-carnitine. These results suggest that propionyl-L-carnitine and acetyl-L-carnitine decrease the cytoplasmic calcium level in endothelial cells.