The Sensex at the Bombay Stock Exchange, which opened in the green today but fell in the negative territory in late morning deals, was trading 42 points down at 18,387 in afternoon trade, when reports last came in. The 30-share index rose by 85 points in opening trade at 18,513, after gaining almost 275 points in the previous two sessions. In a similar fashion, the wide-based Nifty of the National Stock Exchange was trading 17 points down at 5,590.