Abstract: There is disclosed an apparatus for the selective detection and controlled gain of intranuclear and intracellular potentials. Such apparatus contains an amplifier with a gain control, such amplifier having an input terminal and an output terminal and several stages each containing an integrated active electronic device. The input terminal is the input terminal of the integrated active device of the first stage, such input terminal being directly coupled by a double screened lead with a metallic microelectrode for collecting intracell and intranuclear biopotentials.