OKT3 is a murine monoclonal antibody used for immunosuppression of solid-organ transplant rejection. We studied severe visual loss after administration of OKT3 in two patients who received renal transplants (one 25-year-old woman with interstitial nephritis and severe hypertension and one 27-year-old woman with diabetic nephropathy). Both patients lost visual acuity to the level of light perception after a second or third dose of OKT3. Ophthalmoscopy disclosed arteriolar constriction, but there was no evidence of optic atrophy. The electroretinogram was extinguished in one patient, indicating an effect on the outer retina or retinal pigment epithelium. Ophthalmologists should be aware that OKT3 may cause profound visual loss in patients who receive organ transplants.