On July 1, 2002, the Taiwan Stock Exchange changed its closing price procedure to a five-minute call auction. This paper examines different types of trader behavior at the close before and after institution of the new mechanism. The results show that, since the new mechanism was introduced, individuals have shifted their trades away from the closing interval to the preclosing interval, which worsens market liquidity at the close. This paper also finds that institutional investors try to influence closing prices for window dressing at quarter ends, whereas foreign institutions attempt to influence closing prices on the expiration days of index futures. After the new mechanism's introduction, neither the expiration-day effect nor the quarter-end-day effect disappeared. Despite this finding, the new mechanism does make it more difficult and costly for traders to attempt to influence the stock price.