The present invention relates compounds of the formula: or pharmaceutically acceptable salts thereof, useful as sodium channel blockers, as well as compositions containing the same, processes for the preparation of the same, and therapeutic methods of use therefore in promoting hydration of mucosal surfaces and the treatment of diseases including cystic fibrosis, chronic obstructive pulmonary disease, asthma, bronchiectasis, acute and chronic bronchitis, emphysema, and pneumonia.