In a group of 25 Ghanian patients on whom trepano-trabeculectomy was performed, 14 patients had glaucoma simplex and 11 patients had glaucoma and onchocerciasis. Light-microscopical examination of tissue obtained at these operations showed: 1. there are no clear differences in the trabecular system between the 2 groups; 2. the post-trabecular outflow system is markedly abnormal in patients with glaucoma and onchocerciasis: there is infiltration round Schlemm's canal, the efferent veins and the vessels in Tenon's capsule. Microfilariae were also demonstrated in Tenon's capsule. In the discussion the necessity for further study is stressed.