Growing investments on Capitol Hill, such as those in the medical-device industry, raise questions about appearances of conflict. Even if lawmakers have done nothing wrong, ethics specialists said, such apparent conflicts are troubling because it is often impossible to know whether the lawmaker is acting in the interest of citizens or their own portfolios. On Wall Street and in federal agencies, the suggestion of a conflict is often the basis for an investigation.

The uncertainty created about lawmakers' motivation undermines confidence in Congress and the political process, the specialists say. More than half of all lawmakers own stock. In the House, the number of lawmakers trading stock jumped from 91 in 2001 to 259 today, according to academic researchers and the nonprofit Center for Responsive Politics. That includes 68 lawmakers who, as of the beginning of 2008, individually owned more than $100,000 in stock, not including mutual funds.