Patients with type II, non-insulin-dependent diabetes mellitus (NIDDM) typically are middle-aged or older and often have diabetic retinopathy. The visual acuity of these patients also is likely to be reduced beyond what is normally associated with age. Because Medicaid does not reimburse NIDDM patients for a blood glucose meter unless they are insulin-dependent, many low-income diabetes patients are required to monitor their blood glucose levels by visually comparing the color spot on the blood glucose test strip with a series of standard color blocks. Unless patients can accurately assess their blood glucose levels by visual interpretation of the test strips, they will have difficulty maintaining adequate glycemic control. In this study, 60 nondiabetic adults, ages 20 to 78 years, were unable to adequately assess blood glucose levels visually, even under optimal lighting conditions. Younger adults made the same number of errors as older adults, and poor visual acuity and high blood glucose values were associated with more errors. These findings suggest that patients with poor visual acuity or those who read their blood glucose strips in less-than-adequate lighting will make even more errors than our test subjects.