Dapiprazole produces miosis by blocking the alpha 1 receptors in the radial muscle of the iris; its intraocular effect has not yet been investigated. In this preliminary experimental animal study, we investigated the intracameral use of 0.2 ml of 0.005%, 0.0075%, 0.01%, and 0.05% dapiprazole to reverse mydriasis by 10% phenylephrine plus 0.5% tropicamide. With the 0.05% dapiprazole concentration, the values (mean +/- S.E.) of pupillary diameter were as follows: prior to the experiment, 5.3 +/- 0.31 mm; after mydriatics, 8.7 +/- 0.22 mm; after intraocular dapiprazole, 5.6 mm +/- 0.29. The results showed a dose-related miotic effect of dapiprazole. No difference in the toxicity parameters (inflammatory score, corneal thickness, endothelial cell counting, aqueous humor protein concentration, and intraocular pressure) was found between dapiprazole-treated eyes and saline-solution-treated eyes. Intraocular 0.01% and 0.05% dapiprazole is an effective miotic agent that may be helpful during surgery when the reversal of sympathomimetic mydriasis is needed.