A low-noise, galvanic isolated amplifier to be used in conjunction with electrode systems located in sea water has been developed. The objective was to replace an older amplifier (PY 355) with a new one, which (i) is smaller in size and thereby more useful for various applications, (ii) has a broader bandwidth, (iii) at least has a noise level that does not exceed the one of the old amplifier, and (iv) is able to drive the amplified signals through long cables. The amplifier has a very low level of self generated noise (1nV/vHz>1Hz) and is suited for low resistance sensors in the order of 10-50 Ohms. The frequency range is 5 mHz to 14 kHz, with an amplification of 10000 times. An isolation amplifier is included in the unit and provides complite galvanic isolation between the low noise amplifier and the output stage. This means that there is no electrical (or galvanic) contact between sensors or to other amplifiers. The amplifier is equipped with a differential output for balanced transmission of amplified signals on electrical wires. The transmission has been tested on a 2700 m long cable and the upper cut-off frequency for this cable used in conjunction with the amplifier was found to be 11 kHz.