The Sensex at the Bombay Stoc Exchange gained 80 points, or 0.5 per cent, to 17,484 in opening trade, this morning, on continued buying by funds and retail investors. Later, the Sensex remained firm, and stood 99 points, or 0.6 per cent in the positive zone, at 17,503 in afternoon deals, a short while ago.Other regional stock indices in Japan, Indonesia, Singapore and South Korea were up by between 0.2 percent and 0.8 percent, today.