PURPOSE. We evaluated the effects of lentivirus-mediated exoenzyme C3 transferase (C3) expression on cultured primary human trabecular meshwork (1ITM) cells in vitro, and on rat intraocular pressure (10P). METHODS. HTM cells were cultured and treated with lentivirus vectors expressing either green fluorescent protein (GFP) only (LV-GFP) or GFP and C3 together (LV-C3-GFP). Changes in cell morphology and actin stress fibers were assessed. The vectors were also injected into the anterior chamber of rats, and GFP expression was visualized by a Micron Ill Retinal Imaging Microscope in vivo and a fluorescence microscope ex vivo. Changes in rat 10P were monitored by using a rebound tonometer and the eyes were evaluated by slit lamp. RESULTS. LV-mediated C3 expression induced morphologic changes in HTM cells. The cells became retracted and rounded. GFP expression in the anterior chamber angle of rats was observed in vivo from 8 days to 48 days after injection of IN-C3-GFP or IN-GFP loP was significantly decreased in the LV-C3-GFP group starting 3 days post injection, and lasting for at least 40 days, when compared to either the contralateral control eyes (the LV-GFP group) or the ipsilateral baseline before injection (P < 0.05). No obvious inflammatory signs were observed in either the LV-C3-GFP or LV-GFP groups. CONCLUSION. IN-mediated C3 expression induced changes in morphology f cultured 1- M cells. Intracameral injection of LV-C3-GFP lowered rat 10P for at least 40 days. No significant inflammatory reactions were observed in either the LV-C3-GFP or LV-GFP groups. This study supports the possible use of C3 gene therapy for the treatment of glaucoma.