Schering-Plough's (NYSE: SGP) topsy-turvy trading last week drew the attention of more than just investors: It seems the Securities and Exchange Commission is interested enough in what happened to make a few inquiries. Before Schering shareholders panic, however, this is one SEC investigation that should have no effect on the stock price.

The problem arose when the stock began to plummet last week, falling over 15% from Tuesday through Thursday. This drop followed a meeting company executives had with at least one large shareholder, and meetings with other investors and analysts continued throughout the week, as well. Then, after the bell Thursday, the drug maker abruptly warned that its third-quarter and full-year earnings would be sharply lower than expected.

That's when the smaller investors began to yell. Did Schering tip the big guys about the warning ahead of time? According to The Wall Street Journal, a single five-million-share block was traded Tuesday afternoon, which is about what the stock normally trades during a full day. On top of that, volume was well above normal levels Tuesday through Thursday. Was that the result of some mutual funds or institutions selling?

If large shareholders and analysts were told before the warning was issued, it would, of course, be a violation of Regulation FD, the "fair disclosure" rule. The company denies any wrongdoing and says it "welcomes the opportunity to cooperate with the Commission in answering any questions, and believes that it has complied with all applicable securities laws in this matter."

It's doubtful that management intentionally violated the fair disclosure rule. The Journal says some of CEO Richard Kogan's comments to analysts during a private meeting on Thursday may have been misinterpreted, and the company therefore rushed to issue the earnings warning that evening.

At any rate, Schering's handling of this matter is sloppy, at best, and its actions do nothing to ease investor perception that the small guys are still always the last to know about trouble -- some two years after Reg FD was enacted.