The radiosensitivity of cultured bovine lens epithelial cells was measured. Data are given as survival curves for immediate plating (IP) and delayed plating (LP) after a recovery period of 48 h and for plating of cells irradiated in the exponential stage of growth (Exp). The survival curves obtained are strongly exponential, showing no shoulders in the low-dose range, with D37 values of 1.38 (Exp), 2.08 (IP) and 3.28 (LP), respectively. Data of in vitro radiosensitivity are discussed in relation to lens radiosensitivity in vivo. The study was possible by introducing poly-L-lysine hydrobromide coating of culture dishes.