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The aim of this study was to employ an experimental protocol for in vivo evaluation of sols of 5 wt.\% poly(ethylene glycol) (PEG) in phosphate buffered saline (PBS) as artificial vitreous substitutes. A 20 gauge pars plana vitrectomy and posterior vitreous detachment were performed in the right eye of 8 pigmented rabbits. Approximately 1 mL of the viscoelastic PEG sols were then injected into the vitreous space of 6 eyes. PEG with an average molecular weight of 300,000 g mol(-1) and 400,000 g mol(-1) was used in 2 and 4 eyes respectively. Two eyes received balanced salt solution (BSS) and served as controls. Full-field electroretinography (ERG) and intraocular pressure (IOP, palpation) was measured pre-and post-operatively at regular intervals up to 41 days. The rabbits were sacrificed and the eyes were examined by retinal photography, gross macroscopic examination and histology. The viscoelastic sols were successfully injected and remained translucent throughout the postoperative period, with some inferior formation of precipitates. None of the eyes displayed IOP elevation postoperatively, but in 3 of the PEG sol injected eyes, transient hypotony was noted. One eye sustained a retinal detachment during surgery and another 2 in the postoperative period. ERG recordings confirmed preservation of retinal function in 3 out of 4 eyes injected with 400,000 g mol(-1) PEG. Histological examination revealed upregulation of glial acidic fibrillary protein (GFAP) in Müller cells in PEG sol injected eyes, but normal overall morphology in eyes with attached retinas. The viscosity of the sol was not retained throughout the postoperative period, indicating the demand for polymer crosslinking to increase residence time. The results provide promising preliminary results of the use of PEG hydrogels as a vitreous substitute.