A method was developed for determining the velocity of macular blood flow. Leukocytes flowing in the macular capillaries can be recognized when the retina is illuminated with blue light (blue field entoptic phenomenon). The motion of the leukocytes was simulated by a personal-computer system. The velocity of the macular blood flow was determined by adjusting the motion of the simulated corpuscles to that of the entoptically recognized leukocytes. The velocity of the maximum, minimum and mean macular blood flow were measured as 1.25 +/- 0.25, 0.42 +/- 0.11 and 0.80 +/- 0.14 mm/sec respectively. The mean coefficients of variation were 6.7%, 13.4% and 5.7% for each velocity. This method may be useful for the analysis of the retinal circulation and the diagnosis of retinal diseases.