The aim of the this study is to present some performance tests of a novel 256-channel electroencephalographic data-acquisition system. The common mode rejection ratio of the system was measured as 102 dB for signals in the electroencephalography frequency range and 154 dB for de signals. System electrical noise (referred-to-input) is 1.76 mu V (rms) (0.21 mu V/root Hz for 70-Hz bandwidth). The cross-talk rejection was found to be at 58 dB. The dynamic range of the system was found 108 dB. The performance tests and recorded experimental EEG data show that the developed system can be used in conducting source localization experiments.