Purpose Nitric oxide (NO) is among the most important regulators of ocular perfusion. L-arginine, an amino acid, is the precursor of NO synthesis. The aim of the present study was to determine whether administration of L-arginine affects ocular blood flow. Design L-arginine (1 g/min) or placebo was administered intravenously for 30 minutes in 12 healthy volunteers in a randomized, double-masked, two-way cross-over design. Methods Ocular hemodynamics were measured before, in the last 10 minutes of the infusion period, as well as 30 minutes after cessation of the administration. Retinal vessel diameters were measured with a retinal vessel analyzer, red blood cell velocities with bidirectional laser Doppler velocimetry, and pulsatile choroidal blood flow was measured using laser interferometry. Results L-arginine significantly decreased mean arterial pressure by −8 ± 5% and −6 ± 7% at the two time points ( P < .01), respectively. Intravenous administration of L-arginine increased choroidal blood flow by +10 ± 6% and +12 ± 7%, respectively. Retinal venous diameters decreased by −2.5 ± 2.1% and −1.4 ± 2.7%, respectively, whereas red blood cell velocity significantly increased after administration of L-arginine by +22 ± 23% and +20 ± 19% at the two time points. Thus, calculated blood flow in retinal veins, increased by +21 ± 18% and +21 ± 19% before and after the end of L-arginine infusion. Conclusions Intravenous administration of L-arginine increases retinal and choroidal blood flow in healthy volunteers. Whether this effect is related to an increased NO-production or an unidentified mechanism remains to be clarified. However, administration of L-arginine might be an interesting new approach to therapeutically increase ocular blood flow in ocular vascular disease.