I use a time-varying parameter model in order to study the predictability of monthly real stock returns in Germany over the period 1880-1913. I find that the extent to which returns were predictable underwent significant changes over time. Specifically, predictability of returns, as measured by their first-order autocorrelation coefficient, was positive most of the time. It tended to be significant during extended periods of stock market decline, but not during periods of stock market increase. I argue that this time-pattern of predictability of returns is consistent with feedback effects of futures trading on the spot market.