We used monoclonal antibodies against specific T cell, B cell, and macrophage antigens to detect immune system cells in the vitreous gel of retinitis pigmentosa patients. Vitreous samples were obtained by biopsy from three patients and by dissection from eight postmortem donor eyes. All samples contained CD4, T helper and CD8, suppressor cells, activated T cells, some B cells, and macrophages. About one third of the cells were nonreactive. Vitreous gel from normal controls contained mostly nonreactive cells with a few macrophages and rare T cells. These observations further indicated the nature of the cellular reaction in retinitis pigmentosa and characterized the biomicroscopically visible particulate bodies characteristically seen in the vitreous gel of these patients.