The ocular disposition of hydrated 111In-labelled microspheres was investigated in the rabbit by gamma scintigraphy. Microspheres of cross-linked poly(acrylic acid) (Carbopol 907) were prepared by a w/o emulsification process. An in-vitro mucoadhesion test of prehydrated microspheres showed that greater adhesion was achieved to a mucus gel at pH 5.0 compared with pH 7.4. Clearance was a biphasic process with a rapid initial phase preceding a slower basal phase. When hydrated in pH 5.0 phosphate buffered saline, clearance during the basal phase was slowed compared with a pH 7.4 buffered preparation. Both prehydrated preparations were retained on the preocular area during the basal phase for longer periods than non-hydrated microspheres. The retention on the ocular surface of approximately 25% of the instilled dose would suggest this technology will have application for controlled ophthalmic drug delivery.