This paper analyzes the behavior of stock prices around ex-dividend days after the implementation of the 1986 Tax Reform Act that dramatically reduced the difference between the tax treatment of realized long-term capital gains and dividend income in 1987 and completely eliminated the differential in 1988. We show that this tax change had no effect on the ex-dividend stock price behavior, which is consistent with the hypothesis that long-term individual investors have no significant effect on ex-day stock prices during this time period. The results indicate that the activity of short-term traders and corporate traders dominates the price determination on the ex-day.