Transcorneoscleral iontophoresis was used to enhance ocular penetration of a 21-bp NH2, protected anti-NOSII oligonucleotides (ODNs) (fluorescein or infrared-41 labeled) in Lewis rats. Both histochemical localization and acrylamide sequencing gels were used. To evaluate the potential to down-regulate NOSH expression in the rat model of endotoxin-induced uveitis (EIU), anti-sense NOSH ODN, scrambled ODN or saline were iontophorezed into these animals' eyes. Iontophoresis facilitated the penetration of intact ODNs into the intraocular tissues of the rat eye and only the eyes receiving ODNs and electrical current demonstrated intact ODNs within the ocular tissues of both segments of the eye. Iontophoresis of anti-NOSII ODN significantly down-regulated the expression of NOSH expression in iris/ciliary body compared to the saline or scrambled ODN treated eyes. Nitrite production was also significantly reduced in the anti-NOSH applied eyes compared to those treated with saline. Using this system, intraocular delivery of ODNs can be significantly enhanced increasing the potential for successful gene therapy for human eye diseases. (C) 2002 Elsevier Science (USA). All rights reserved.