[en] We have tested the radiation resistance of two 10 cm long CsI (Tl) crystals in the radiation environment of the PETRA e⁺e^- storage ring. The crystals were exposed for 38 days to an average dose of 50 rad and 20 rad, respectively. The exposure lead to a continuous decrease of pulse height with a final reduction of 13 +- 1% (crystal 1 with photodiode readout at 50 rad) and 19.5 +- 2% (crystal 2 with photomultiplier readout at 20 adout at 20 rad). Most of the damage occurred in the first days of exposure. After the end of the exposure we observed a partial recovery of few percent. (orig.)