Subcutaneously administered Cd2+ (in vivo) was accumulated in the eyes of rabbits. The concentration was greatest in the iris-ciliary body, followed by the retina, cornea, and lens. It was also present in the vitreous humor, but was not detectable in the aqueous humor. Cd2+ in the bathing medium in vitro was toxic to the lens (tissues gained Na and lost K) at 10(-3) M, for 24 hr incubation, or 10(-5) M, for 7 days. Cadmium-109 was gradually accumulated by the lens in vitro (the process may be saturable), but with 10(-7) M Cd in the medium (similar to the vitreous in Cd-treated rabbits) 100 times less was taken up in 24 hr than in the 28-day in vivo experiments. Cadmium-109 in vitro was almost confined to the outer 30 to 50% of the lens tissue. Cadmium-109 was able to reenter the bathing medium, and its efflux was not changed by the presence of external Cd, suggesting that substantial specific binding was not occurring. Efflux could be reduced by lanthanum so that it may follow pathways similar to those used by Ca and Zn.