The electrical response of Pt microelectrodes, with a radius of 10 mu m, was studied in liquid ammonia (- 50 degrees C). The question of a suitable tune stale for steady state measurements in liquid ammonia is important. The proton reduction currents were measured for different scan rates. A suitable experimental time scale of 20 mV s (-1) was determined to reach a stationary state. The diffusion coefficient of protons in liquid ammonia was deduced from these electrochemical results: D(NH4+)(NH3) = (3.8 +/- 0.4) x 10(-9) m(2) s(-1) .