The Sensex at the Bombay Stock Exchange was trading 21 points in negative territory at 18,521 a short while ago. Earlier the BSE benchmark Sensex fell by over 61 points in early trade today as funds and retail investors indulged in profit-booking at prevailing higher levels amid weak trend in Asian markets. The 30-share index fell by 61 points, to 18,480 with stocks of metal, auto and banking sectors leading the fall.Similarly, the wide-based National Stock Exchange index Nifty declined by 6 points to 5,603.