Remaining weak in afternoon trade, the Sensex at the Bombay Stock Exchange stood 173 points, or 0.8 percent in negative territory, at 21,066, a short while ago. Earlier in the morning, the Sensex had fallen 105 points, or 0.5 per cent, to 21,134, as funds and retail investors booked profits, amid weakness in the regional bourses. The 30-share Sensex had gained almost 670 points in the previous five trading sessions. Stock markets in China, Hong Kong, Taiwan, and South Korea had dropped between 0.4 percent and 0.8 percent, today. The US Dow Jones Industrial Average had added 0.2 percent in yesterday's trade.