A simple circuit for use in conjunction with electrometer tubes is described. This configuration provides for a reduction in the input capacitance of the circuit to a value in the order of 0.05 (Cgk+Cgp) of the electrometer tube. At the same time linearity is improved. These qualities are achieved through causing both the cathode and the plate potentials of the electrometer tube to follow its grid. No critical compensating adjustments are required. This circuit is particularly suitable as a preamplifier for electrophysiological measurements.