The article discusses how changes in the supply of U.S. Treasury securities can affect bond and stock markets. Over the past 80 years, supply risk has added about 13 basis points to the real rate of return on T-bills, down from 36 basis points before 1946. Inflation risk has also decreased, from nearly 5.5 percentage points to 1% in the last 20 years. When T-bill supply increases, their price drops and their return rises, affecting stock prices slightly. However, stock returns are negatively correlated with T-bill rates, suggesting that the bond and stock markets are somewhat separate. The share of bonds in the U.S. Treasury portfolio increased until the end of World War II, then declined steadily.