Oxidative stress plays a key role in vascular diseases such as hypertension, atherosclerosis, diabetes mellitus and cardiomyopathy. This occurs when intracellular levels of reactive oxygen species (ROS) increase, decreasing the bioavailability of nitric oxide (NO), a vasodilator synthesized from L-arginine (Sobrevia & González, 2009). This amino acid is incorporated into endothelial cells by cationic amino acid transporters (hCAT-1 and hCAT-2B) (González et al., 2004). The effects of ROS on activity and/or expression of hCATs are not fully understood. Our aim was determine the effects of chronic incubation with hydrogen peroxide (H2O2) on hCATs expression and L-arginine transport in human endothelium. Biological samples were obtained from normal pregnancies (ethics committee approval and informed patient consent were obtained). Human umbilical vein endothelial cells (HUVEC) were isolated by collagenase digestion (37 celsius degree) and cultured in medium 199 (M199) supplemented with 20% newborn and fetal calf sera. Cells were incubated (24 h) with H2O2 (10-12-10-3 M). The mRNA levels of hCAT-1, hCAT-2B and 28S were determined by real time PCR. The protein abundance of hCAT-1 was determined by western blot. L-Arginine uptake (100 µM) and kinetic parameters of L-arginine transport (31.25-1000 µM L-arginine, 2 µCi/mL L-[3H]arginine) was determined. Results showed that H2O2 (10-12-10-6 M) increased (ANOVA unpaired Student’s t test, P<0.05, n=5-10) the mRNA levels of hCAT-1 and hCAT-2B. The protein abundance of hCAT-1 was decreased (65±13 % from control) by H2O2 (1 µM). H2O2 (0.1 µM) decreased the Vmax of L-arginine transport from 1.6±0.3 (pmol/µg protein/min)(control) to 0.3±0.09 (pmol/µg protein/min), without changes in the apparent Km (100-300 µM). The L-arginine transport capacity (Vmax/Km) was decreased from 12.8±3.2 (fmol/µg protein/min/µM) (control) to 2.3±0.3 (fmol/µg protein/min/µM) by 0.1 µM H2O2. In conclusion, the chronic incubation of HUVECs with H2O2 induces a decrease of L-arginine transport mediated by a lower expression of hCAT-1. However, the mRNA levels of hCAT-1 and hCAT-2B are increased by the same concentration and time of incubation of H2O2. Is possible that the oxidative stress activates a transcriptional mechanism to try to restore the cellular capacity of transport L-arginine for maintenance the cellular metabolism.