Today's 2 Worst Stocks in the S&P 500

The stock market today stood in stark contrast to Wall Street's mood on Monday, when all three major indexes ended solidly in the green. Investors couldn't get too excited today, though, as they wait with bated breath for tomorrow's address from Federal Reserve Chairman Ben Bernanke, who will reveal the rationale behind the central bank's decision to either cut back on quantitative easing measures or keep them in place. Markets lost ground in December's first two weeks as shareholders braced for a possible "tapering" from Mr. Bernanke & Co. The S&P 500 Index fell five points, or 0.3%, to end at 1,781 Tuesday.

Delta Air Lines stock was the most severe decliner in the 500-stock index today, losing 3.5%. Delta also managed to wind up on this list yesterday, though the reasons behind the slump were less tangible. Weather conditions are dogging airliners today as the industry tries to recover from a weekend of more than 1,000 flight cancellations on the heels of wintry weather across the country. Delta sure didn't need one of its flights to slide off the runway at an airport in Wisconsin this afternoon, either, but Mother Nature had her way with the aircraft. The flight had already landed and was taxiing to the gate at the time of the incident, in which no one was injured.

Finally, shares of $25 billion Regeneron Pharmaceuticals stock shed 2.5%, though there weren't any obvious catalysts behind the sudden move. Shares have slumped more than 10% since early December, when one threat to Regeneron's blockbuster Eylea treatment emerged from Ohr Pharmaceutical . Eylea is an eye injection that treats age-related macular degeneration, and Ohr is working on an eye drop that reduces the number of eye injections necessary in treating the ailment. Ohr is also developing its eyedrop to be applicable to one of Regeneron's rivals specifically, making Eylea one step closer to total obsolescence if the product is successful. On top of that, health care was already the worst-performing sector in the markets today, so it's no wonder Regeneron had a rough day.

Editor's note: A previous version of this article included J.C. Penney as part of the S&P 500. The stock is no longer in the index. The Fool regrets the error.

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The article Today's 2 Worst Stocks in the S&P 500 originally appeared on Fool.com.

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