Using a new test, in which patients are asked to view printed sinusoidal gratings of varying contrast, we have established normal population values and have investigated a small series of glaucomatous patients. In these, test scores are higher than the normal range and increase with the severity of the disease. Patients with raised intraocular tension, normal discs, and no field loss may give abnormal results. The test can be scored so that a very sharp distinction may be made between normal and glaucomatous eyes. The test is simple, quick to perform, portable, and can be done in almost any situation.