A secondary immune response in the rabbit eye can be provoked by intravenous injection of the antigen, previously injected intravitreally. The inflammation process consists of iris hyperemia, pericorneal redness and cellular and proteinous exudates in the anterior chamber and vitreous.The influence of vitrectomy combined with lensectomy or preceded by extracapsular lens extraction on the character of the secondary immune response has been studied in the rabbit eye.Both eyes of adult rabbits were injected intravitreally with human serum albumin. Five to ten weeks later, when the primary inflammation process had vanished, the vitreous and the lens were removed from the right eye in one group of animals. In a second group of rabbits, an extracapsular lens extraction was performed upon both eyes, later followed by vitrectomy of the right eye. Four weeks later all animals received an intravenous booster injection with human serum albumin.The eyes which still contained the vitreous developed a secondary inflammation consisting predominantly of cells and fibrin clots in the anterior chamber however without flare. On the contrary, the eyes which underwent vitrectomy developed a flare in the anterior chamber with only a few cells detectable. Analysis of cells and protein in the anterior chamber and histological evaluation supported the clinically observed differences between both eyes.These results suggest that the persistence of the vitreous is associated with the reactivation of a secondary immune response. Vitrectomy combined with lensectomy or preceded by extracapsular lens extraction leads to increased passive transfer of proteinous material through the vessels.