We used magnetic resonance spectroscopy to examine endophthalmitis in rabbits inoculated with a virulent strain of Streptococcus pneumoniae. On different days after infection, the animals were sacrificed and the vitreous isolated and examined with water-suppressed proton magnetic resonance spectroscopy. A broad resonance corresponding to the methyl envelope of lipoprotein lipids appeared 2 days after infection and persisted until the eyes developed phthisis (around 10 days postinfection). This resonance was absent in the control eye and the bacterial culture; it could be used as the marker of breakdown of blood-vitreous barrier and onset of endophthalmitis-induced changes.