The paper investigates the effect of interest policy on price bubbles, trading behavior and portfolio choice in experimental stock markets. A series of experiments has 8 participants trade an asset over 15 periods. Alternatively, the participants can invest money in interest-bearing bonds. Treatment groups are subjected to an endogenous interest policy, while control groups experience a constant interest rate. Our stock markets are characterized by bubbles. While we observe a small positive impact of our interest policy on bubbles, the policy also strongly increases market volatility. On the other hand, concerning portfolio choice, we find evidence for value-driven (rational) investment behavior.