We have described a complex abnormality of retinal pigment epithelium, Bruch's membrane, and choriocapillaris in mesangiocapillary glomerulonephritis (MCGN) type II. Patients with MCGN type II were examined by vitreous fluorophotometry which reveals that there is a breakdown of the blood retinal barrier (BRB) in those patients with the typical fundus lesions. The function of this barrier was calculated as a penetration ratio and was statistically greater in these patients when compared with a group of (a) normal persons, (b) patients with drusen, and (c) patients with other forms of glomerulonephritis.