[en] One of the factors important for the maintenance of eye lens transparence is its water content which is controlled by the active transport of Na⁺ and K⁺ in the lens epithelium. In early phases of ontogenesis the rat lens is highly sensitive to various cataractogenic impulses (e.g., selenium induced cataract). In the present study, the question was studied of whether the ion turn-over in the lens changes during ontogenesis. Experiments were done on Wister rats of age span from 1 prenatal day to 2 years. The uptake was measured of ⁸⁶Rb which in the lens is transported analogously to K⁺. The rats were decapitated and extracted lenses were incubated in a MEM medium supplemented with bovine fetal serum and ⁸⁶Rb. ⁸⁶Rb uptake was expressed as a ratio of ⁸⁶Rb concentration in lens water to its concentration in the medium at the beginning of incubation. The ⁸⁶Rb was found to differ substantially in different age groups. A rapid drop in the uptake of ⁸⁶Rb was found in the lens in the critical period of lens development when the lens grows intensively and displays the highest sensitivity to exogenous metabolic disturbances. The developmental changes in the uptake of ions by the lens can reflect changes in the synthesis of both enzymes and crystallines. (author)