It has been recognized that hydrogen sulfide evolving in biochemical reactions in living organisms has important roles in different physiologic processes. In these days, hydrogen sulfide is known as an endogenous messenger molecule. Several natural sulfurous spring waters have been proved beneficial for treating different skin and internal diseases. In vivo detection of local, instantaneous hydrogen sulfide concentration is an important, but challenging task in certain life science experiments.In our studies an amperometric two electrode micro cell has been developed for selective subcutaneous detection of hydrogen sulfide in anesthetized experimental mice. The cell is a small size implantable gas sensor containing a platinum micro disc anode and a silver cathode. The selectivity is provided by a membrane permeable only for gases. Inside the cell a buffered solution of oxidized form of an electrochemically reversible mediator material is confined. The hydrogen sulfide gas getting into the lumen cell reduces the oxidized form of the mediator. An appropriate constant potential is employed between the two electrodes. The reduced mediator is oxidized on the anode surface. The current is the analytical signal for reflecting the hydrogen sulfide concentration.Appropriate shape, size and membrane material were selected and optimal working parameters, like mediator concentration, pH and cell voltage were worked out in vitro. In stirred sample solution with pH =5.5 lower limit of detection as small as 0.3ppm could be achieved with dynamic concentration range of 0–20ppm could be achieved.The cell surface was covered with freshly dissected mouse skin in order to test the H 2 S permeability of it. Furthermore, the cells were implanted subcutaneously in the anesthetized mice and bathing them in buffer solution (37°C, pH=5.5) containing different concentrations of H 2 S measurements were made. The experiments clearly proved that considerable amount of H 2 S absorbs through the skin of bathing living mice.