The Bombay Stock Exchange benchmark Sensex was trading at 18,529 points, down by 57 points a short while ago. Earlier, the Sensex fell by 125.98 points, or 0.67 per cent, to 18,458.98 in opening trade. The wide-based National Stock Exchange Nifty index was also down by 17 points, trading at 5,548 points when reports last came in.