In an objective test to determine compliance with acetazolamide regimens by patients with glaucoma, treated inpatients had lower carbon dioxide levels (less than or equal to mEq/L) than untreated patients (greater than or equal to 25 mEq/L). The test results may be inaccurate in some obese diabetic patients with hyperglycemia and in some patients with obstructive lung disease, such as asthma and emphysema. In an outpatient clinic population, the test showed that 35% (30/87) of the patients did not seem to be taking acetazolamide and 22% (19/87) seemed to be taking it less frequently.