A biomicroscopical study of the vitreous body was performed on 116 eyes of 58 patients with primary retinitis pigmentosa, and six additional eyes were examined histopathologically. A characteristic vitreous degeneration, found in all eyes, was clinically divided into four sequential stages that appear to parallel the magnitude of gross retinal destruction as determined by visual-field measurements. The vitreous breakdown in retinitis pigmentosa may be due to progressive loss of hyaluronic acid from the hyaluronic acidcollagen complex.