Between 1976 and 1977, 347 lithium powered pacemakers with capacity below 1.8 Ah have been implanted at Zurich University Hospital. 25 (7%) had to be explanted after an average of 37.3 months because of premature battery depletion, the reason for which was low resistance electrodes (Elema EMT 588 A and C) in CPI-502 UD and Telectronics 150B. Both types showed a drop in stimulation rate as an EOL-characteristic, as predicted by manufacturer. Rate controls at 6 month intervals have proven a reliable means of detecting premature failure. With ARCO Li-3D, prediction of battery depletion was possible only in one case out of 5 because of sudden and unpredictable EOL. In pacemaker dependent patients this type should be explanted by the end of the guarantee period at the latest.