Exposure of four monkey and 26 rabbit eyes to neodymium-YAG laser irradiation to the posterior lens capsule or the mid-vitreous area clearly demonstrated significant vitreous changes (liquefaction) as measured by viscosity analyses and proton relaxation studies. We found marked molecular alterations in the vitreous of the exposed eye compared with the contralateral control (unirradiated) eye. These alterations, occurring immediately after laser treatment, were probably the result of acoustic transients accompanying the laser irradiation.