A single filtering operation was performed on 46 eyes of 28 American black patients with varying forms of glaucoma. An operation was considered successful when the intraocular pressure was below 22 mm Hg six months after surgery on no further medications. Of the 36 eyes with six months follow-up eight (22%) had IOP below 22 mm Hg on no further medication. The remaining 28 eyes (78%) required the addition of glaucoma medications to control the pressure. Conjunctival scarring of the filtering bleb occurred rapidly in most failures though the mechanisms by which these closures occur remain obscure. Topical steroids and cycloplegia did not significantly alter the course of this increased failure rate in American blacks.