Retinal blood flow velocity was measured in 24 normal volunteers and compared with the results obtained in 101 diabetics at different stages of retinopathy. The blue-light entoptic phenomenon was used to measure retinal flow velocity. Results showed that there was a significantly higher capillary flow velocity in those patients with background retinopathy (0.74 +/- 0.32 mms/s) over the group of normals (0.54 +/- 0.19 mm/s) and those diabetics with no retinopathy (0.51 +/- 0.24 mm/s). Retinal flow velocity was reduced at the preproliferative stage of retinopathy to 0.37 +/- 0.2 mm/s. Proliferative retinopathy showed a slightly greater flow velocity (0.56 +/- 0.27 mm/s), which was reduced following photocoagulation (0.42 +/- 0.14 mm/s).