Administration of low doses of Escherichia coli endotoxin (LPS) to humans enables the study of inflammatory mechanisms. The purpose of the present study was to investigate if the blue field entoptic technique may be used to quantify the increase of circulating leukocytes after LPS infusion in the ocular microvasculature. In addition, combined laser Doppler velocimetry and retinal vessel size measurement was used to study red blood cell movement. 12 healthy male volunteers received 20 IU/kg LPS as an intravenous bolus infusion. Outcome parameters were measured at baseline and 4 hours after LPS administration. In the first protocol ocular hemodynamic effects were assessed with the blue-field entoptic technique, the retinal vessel analyzer and laser Doppler velocimetry (n=6). In the second protocol white blood cell counts from peripheral blood samples and measurements with the blue field entoptic technique were done (n=6). LPS caused peripheral blood leukocytosis and increased white blood cell density in ocular microvessels (+49%; p = 0.036), but did not change white blood cell velocity. In addition, retinal venous diameter was increased (+9 %; p = 0.008), but red blood cell velocity remained unchanged. The LPS-induced changes in retinal white blood cell density and leukocyte counts were significantly correlated (r = 0.87). The present study indicates that the blue field entoptic technique can be used to assess microvascular leukocyte recruitment in vivo. In addition, our data indicate retinal venous dilation in response to endotoxin.