The purpose of this experiment was to study in vivo the dynamic behavior of the lymphocyte in the retinal circulation. We developed a new technique capable of visualization of lymphocyte motion in the retinal and choroidal vessels using a rat model. Live cells freshly removed on a donor animal were labeled by a simple method using fluorescein isothiocyanate. Labeled cells were injected systemically into another animal. Retinal images were reconstituted on a video screen with a scanning laser ophthalmoscope (SLO) utilizing the argon green laser excitation wavelength (514.5 nm) to detect cell fluorescence. Lymphocytes were clearly seen and followed in the retinal vessels. Some slowed down in the capillary system, or even stopped for a few seconds, or were definitively caught in it. Labeled cells remained visible after circulating several times. A method was developed for in vivo visualization of lymphocytes in the retinal circulation. This method has the potential for application in the study of lymphocyte cell behavior under physiological as well as pathological conditions.