A technique for transvitreal chorioretinal biopsy has been developed which employs a stereotaxic intraocular micromanipulator and a newly designed biopsy instrument. Biopsy is performed by trephinating and removing from the eye a 1.5-mm diameter specimen of posterior eye wall. Hemostasis and chorioretinal adhesion are achieved by mechanical compression of the tissues surrounding the eye wall defect. The eye wall defect is sealed by a preplaced silicone explant and repaired by fibrovascular ingrowth from the surrounding choroid and episclera. Normal histological features of the biopsy specimen are preserved except for edema of the tissues, separation of the neurosensory retina from the pigmented epithelium, and occasional hemorrhagic detachment of the pigmented epithelium.