Alginic acid was evaluated as a potential vehicle in ophthalmic solutions for prolonging the therapeutic effect of carteolol. This anionic vehicle was expected to slow down drug elimination by the lacrimal flow, both by undergoing in-situ gel formation and by interacting with the mucus. In vitro studies indicated that carteolol is released slowly from alginic acid formulations, suggesting an ionic interaction. The adhesive behavior of alginic acid solution was better than that of another polymer, hydroxyethylcellulose (HEC). Intraocular pressure (IOP) measurements of rabbit eyes treated with a 1% carteolol formulation with or without alginic acid showed that this polymer significantly extended the duration of the pressure-reducing effect of carteolol to 8 h. The increased ocular bioavailability of 1% carteolol in the presence of alginic acid led to an equivalent concentration in the target tissue although administration was only once a day compared with twice a day for 1% carteolol alone. The overall results of this study indicate that the alginic-acid vehicle is an excellent drug carrier, well tolerated, and could be used for the development of a long-acting ophthalmic formulation of carteolol.