The high-frequency resistance of tin in the superconducting state was measured at a wave-length of 20$\cdot $5 cm. by a calorimetric method based on the principle of eddy-current heating. It was found that the resistance decreases gradually when the temperature falls below the transition point in contrast to the sudden drop in resistance peculiar to direct currents. An explanation of such a behaviour is given based on the assumption of the simultaneous presence of normal and superconducting electrons. Good agreement between theory and experiment was found. Absolute measurements of the conductivity in the normal state at low temperatures with both high and low frequencies were carried out, and it was found that at the temperature of liquid helium the conductivity for high frequency is considerably lower than for low frequency. This behaviour is possibly due to the fact that the mean free path of the electrons becomes larger than the penetration depth due to skin effect under the conditions of high conductivity and high frequency.