The movements of plastic microspheres (7 to 10 mu in diameter) and autologous RBCs labeled with sodium chromate Cr 51 from the vitreous to the anterior chamber were studied in 24 rabbit eyes. Rabbits were made aphakic in one eye by intracapsular lens extraction of lensectomy via the pars plana, the fellow eyes serving as phakic controls. In phakic eyes the intravitreally injected microspheres and RBCs were retained inside the vitreous space, not gaining access to the anterior chamber. In aphakic eyes microspheres and RBCs moved to the anterior chamber and were usually seen on the corneal endothelium and in the chamber angle within two to ten days, although most particles remained in the vitreous for long periods of time. Removal of the lens thus improved forward drainage of particles from the vitreous space, but the structure of the vitreous seemed to preclude rapid clearance.