A 61-year-old man with a history of cerebral reticulum cell sarcoma-microglioma (histiocytic lymphoma) in remission was initially seen with uveitis and exudative retinal detachment. Pars plana vitreous biopsy established the diagnosis by cytologic findings and allowed the immunofluorescent demonstration of a monoclonal immunoglobulin within the vitreous cells. Direct immunofluorescent microscopy of the vitreous infiltrate may prove to be of benefit in the workup of patients with uveitis in whom malignant lymphoma must be excluded.