A slump in major stocks like HDFC Bank, ICICI Bank and Reliance Industries weighed on the market and the equity benchmark Sensex opened the day 150 points down. The 30-share BSE index was trading 186.94 points or 0.38 per cent lower at 49,559.27 in the opening trade, while the broader NSE Nifty slipped 44.10 points or 0.30 per cent to 14,829.70.