Tritium content was measured in snow deposited in Antarctica before the first arrival of artificial tritium (1954), both at Dome C (74¿39'S) and South Pole. The mean tritium values at the time of precipitation are equal to 32¿2 and 26¿3 TU at South Pole (1939-1942) and Dome C (1951) respectively. A seasonal pattern of natural tritium fallout identical to the artificial pattern (with a winter maximum) is observed in the South Pole profile. The deposition rate of natural tritium is 0.6 and 0.2 tritium atoms cm-2. sec-1 at South Pole and Dome C respectively. Its geographical variation over Antarctica appears quite similar to that existing for artifical tritium, clearly showing that the same mechanisms govern the deposition of natural and artificial tritium, in particular tritium injection over polar regions during Antarctic winter. A mean deposition rate of 0.37 tritium atoms cm-2. sec-1, over Antarctica is derived giving an estimated mean global production rate of 0.2 tritium atoms cm-2. sec-1. This strongly suggests that natural tritium results only from cosmic ray production.