Abstract 1.1. Results on eighteen healthy individuals indicate that neither sulfathiazole, sulfadiazine, nor sulfanilamide significantly alters dark adaptation time as measured by the Feldman adaptometer. 2.2. There is an indication, however, that those subjects which received sulfanilamide exhibited enough increase in their dark adaptation times to suggest a possibility that this sulfonamide may have a direct effect upon dark adaptation. 3.3. These experiments would not corroborate the general opinion that persons taking small doses of sulfonamides daily need necessarily be concerned about visual acuity or efficiency.