TENNESSEE Republican Bill Frist has been a senator for almost 11 years now, majority leader for three. During his tenure, Mr. Frist, a heart surgeon, has worked on -- and often taken a leading role in -- such health care issues as the Medicare prescription drug bill, limits on medical malpractice awards and managed-care legislation.

Throughout that time, Mr. Frist rebuffed suggestions that his extensive holdings in HCA, the giant hospital chain founded by his family, posed any ethical problem. When Democrats denounced this as a "blatant conflict of interest" during his run for a second term, Mr. Frist dismissed those concerns, brandishing opinions from the Senate's Select Committee on Ethics stating that he was free to vote on health care matters despite millions of dollars in HCA holdings. Indeed, Mr. Frist insisted, he had gone the extra ethical mile of putting his holdings in a blind trust.

So it's more than a little curious that Mr. Frist, who will end his Senate career next year, has chosen this time to decide to heed ethics concerns and sell off his HCA holdings. The senator's blind trust turns out to allow for a little peek-a-boo, and Mr. Frist instructed the trustees in June to get rid of the stock. That was good timing: The company's stock price fell 9 percent the next month, after it disclosed lower-than-expected second-quarter profits.

Mr. Frist's spokeswoman, Amy Call, said the move was based "purely on wanting to avoid any future appearances of conflict." But, of course, if that was a problem, why did it take the senator more than a decade to figure it out? After all, any such perception didn't seem to bother Mr. Frist this year, when he championed medical malpractice caps even as his family's hospital empire included a large malpractice insurer.

One possible explanation for Mr. Frist's action is that he is weighing a presidential run and wanted to get any potential ethical issue out of the way. A more conspiratorial explanation comes to mind, as well, which is that Mr. Frist had some advance knowledge of the company's impending bad news. Mr. Frist's brother is HCA's largest individual shareholder, its chairman emeritus and a member of the company's board. There's no evidence that Mr. Frist had inside information or traded on it, though Ms. Call's careful phrasing -- that the senator "did not have any conversations with HCA executives about HCA stock when he was making the decision to divest" -- is curious.

Still, Mr. Frist's sudden and well-timed change of mind about his ethical obligations at least warrants further inquiry; this is the kind of thing the Securities and Exchange Commission does routinely. It ought to do so in this case, too -- if only to clear the senator of the worse of two unflattering possibilities.