Transport of Ca ions across the cornea was studied by the use of 45Ca. The solution containing radioactive Ca was brought in contact with either side of the cornea. The transmission of the film which was exposed to radioactive Ca penetrated into the cornea was determined photoelectrically. The relative flux rate was thus determined. It was found that flux ratio (outflux/influx) is far greater than the theoretical value estimated on the assumption that the transport is carried out by diffusion. The outflux was depressed at low temperature. The metabolic inhibitors such as iodoacetic acid, DNP, NaF, KCN inhibited the outflux. These results seem to indicate the existence of an active transport of Caions from the aqueous humor, across the endothelial cells, to the stromal fluid.