The relative effect of topically administered polysorbate-80 solutions of indoxole and indomethacin were compared as to inhibition of pupillary constriction induced by standard trauma, in the presence of phenylephrine, to the rabbit iris. At all concentrations indoxole maintained mydriasis more effectively than did indomethacin. This difference was statistically significant at the 0.5 and 1.0% dose levels. For both drugs, a concentration of 0.5% yielded close to the maximum dose response. For indoxole, maximal effect was found following a single instillation 60 min before the standardized traumatic maneuver.