Aluminum and platinum foils were flown into two bright auroras and subsequently recovered. They were then analyzed for traces of trapped noble gases in a sensitive high-resolution mass spectrometer. In this paper we report the detection of 3He and confirm measurements of the 4He flux reported in a previous paper. The 4He:3He ratio in the first (brighter) aurora was 2950¿250. This ratio is only slightly higher than the average solar wind ratio of 2350 and since the atmospheric ratio is grossly different (250 times larger), establishes the solar wind as the principal source of auroral helium, at least in the aurora concerned. The result supports earlier suggestions that auroral precipitation is one of the main sources of the 3He in the terrestrial atmosphere. Current estimates of 3He sources and loss rates are found to be consistent with a balanced atmospheric 3He budget.