Here we provide a range of reusable and disposable passive biopotential electrodes for EEG, EOG, ECG, surface EMG, skin conductance / resistance and skin potential measurements.  We offer both Ag/AgCl (Silver/Silver-Chloride) and Gold electrodes in certain product configurations.  In general, Ag/AgCl has the most desirable electrical properties, being essentially non-polarizable, DC-stable, resistant to scratching, relatively durable, maintenance-free, etc.  Gold electrodes do last longer than Ag/AgCl, but they are relatively expensive and have larger DC offset potentials.