1. DIDS (4,4'-diisothiocyano-2,2'-stilbene disulphonic acid) reduced the CI Isc across the toad's (Bufo marinus) cornea. It acted on either the aqueous or tear side and these effects were additive. 2. The reduction in the Isc was equivalent to the decline in the undirectional flux of Cl from the aqueous to the tear side. The Cl flux from tear to aqueous was not changed. 3. DIDS did not change transmural Na transport. 4. The action of the diuretic bumetanide, which also inhibits Cl transport was additive to that of DIDS when both compounds were present on the aqueous though not when they were on the tear side of the cornea. 5. The results are consistent with the role of a Cl-/anion exchange mechanism in active Cl transport across the cornea. 6. A hypothesis regarding the interactions and site of action of bumetanide in relation to that of DIDS, and the Cl transport process, is proposed.