Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of biopharma company Repligen (Nasdaq: RGEN) sunk as much as 31% in intraday trading on heavier-than-average volume.

So what: Pop quiz: What can possibly make a drug developer drop this much in a day? If you said, "Bad news about one of its drugs," go ahead and affix a gold star to your forehead. Today, Repligen released results from its Phase II study on RG2417, a potential bipolar depression treatment. The results showed that overall, there was no statistically significant improvement in patients versus a placebo over the eight-week trial. That doesn't make for promising marketing materials.

Now what: The company did note that a smaller group of the patients who were in academic medical centers -- as opposed to commercial sites -- did show significant results, so there could be a spark of hope for RG2417, but it still doesn't seem very promising. The company tried to be as upbeat as possible in its press release, though, and pointed to its other products in development as well as its focus on maintaining its strong balance sheet.

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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.