That sulfanilamide and its derivatives have attained a secure position as therapeutic agents for the treatment of certain ocular infections is attested by numerous reports. Of these, sulfanilamide (paraaminobenzenesulfonamide, sulfapyridine (2- [paraaminobenzenesulfonamido]-pyridine) and sulfathiazole (2-sulfanilamidothiazole) have been employed most extensively. Experimental justification for the use of sulfanilamide and sulfapyridine in the eye lies in the ready penetration of these compounds into the ocular tissues and fluids in concentrations approximating that of the blood.1 Thus far, despite the clinical use of sulfathiazole, no experimental evidence has been presented to show that it reaches the eye. If this drug shows a penetrability similar to that of the other two it should prove a valuable adjunct in ocular therapy. It is superior to sulfapyridine in its ready intestinal absorption and is less toxic.2 Nausea and vomiting are less than with sulfapyridine, although dermatitis is more frequently encountered.3 Experimentally its effectiveness