The effects of moisture stress on Valencia peanut (hypogaea L.) yields were evaluated on Fox loamy-sand soils (Typic Hapudalf or Brunisolic Gray Brown Luvisols); of southwestern Ontario. Drought-imposed irrigation experiments were conducted in 1980 and 1981 by withholding water over all possible combinations of three peanut growth periods, as follows: Period I, early and full flowering; Period 2, late flowering and pod formation; Period 3, pod filling. Generally, the results indicated that the period of late flowering and pod formation is most sensitive to moisture and that moisture stress in growth periods 2 and 3 reduced yields more than stress in periods 1 and 2. Year-to-year variations indicated that, at least in this short-season growing area, factors other than moisture stress alone were influencing peanut yield and quality.