We designed a new device, a scleral plug, that releases drugs into the vitreous after being implanted and fixed at the pars plana. Use of the plug for provision of doxorubicin hydrochloride was evaluated in rabbits. The scleral plug (8.5 mg) was made of poly(lactic-glycolic acid) (molecular weight, 40,000 daltons) containing 1% doxorubicin. Vitreous concentrations of doxorubicin were measured after the implantation. In vitro studies showed that the plug released 26% of the drug during 4 weeks. In vivo studies demonstrated that the concentration in the vitreous humor was maintained at a therapeutic range for longer than 4 weeks. No substantial toxic reactions were observed by electroretinographic and histopathologic evaluations. Our findings suggested that a scleral plug made of biodegradable polymers is a promising device for a controlled drug-release system in the vitreous.