Two cases of pseudo-Brown's syndrome occurring after superior nasal implantation of glaucoma filtering devices are described. We hypothesize that this restriction in ocular motility was due to the mechanical effects of large filtering blebs or increased inflammation and scar formation in the superior nasal quadrant. Serial ultrasound examinations of our patients demonstrated development of a large bleb, coincidental with the disturbance in motility. Because of the risk of strabismus, we no longer recommend placing large implant devices in the superior nasal quadrant in eyes that have good vision.