The Sensex at the Bombay Stock Exchange rose 86 points, or 0.5 per cent, to 17,939 in opening trade, this morning, on sustained buying by funds and retail investors ahead of domestic industrial output data, and amid positive Asian markets. Later, the Sensex remained firm, and stood 64 points, or 0.4 percent in positive territory, at 17,917 in afternoon deals, a short while ago. The 30-share Sensex had gained over 540 points in the past five trading sessions.Key stock indices in Japan, Singapore, Taiwan, South Korea, Hong Kong and Indonesia were up by between 0.3 percent and 1.5 percent, today. The US Dow Jones Industrial Average had ended 0.5 per cent higher in yesterday's trade.