As the presidential campaign narrows and its costs skyrocket, detailed disclosure of financial resources becomes ever more important. Of the leading contenders, so far, only Senator Barack Obama has released his full income-tax returns  a level of disclosure once routine for candidates after the political corruption of Watergate.

Release of the tax returns should not be made conditional on winning the nomination, as Senator Hillary Rodham Clinton has made it. Both Senator John McCain, the Republican front-runner, and she owe it to their parties and to voters to promptly make available their Internal Revenue Service filings, and to respond to any questions about them. It is true that as senators, Mrs. Clinton and Mr. McCain are required to file financial disclosure forms. But those forms present only general parameters of family financial resources, not the detail available on tax returns.

The need for greater transparency regarding the income and overall financial dealings of candidates and their spouses was underscored by Mrs. Clinton’s recent decision to make a $5 million loan to her campaign. Such borrowing is a permitted practice under the campaign laws. But the campaign said the money came from her share of the Clintons’ joint resources, and that calls attention to the lack of information about their family finances. As a former president, Bill Clinton has been making millions annually giving speeches and traveling the globe. What is publicly known about his business dealings is sketchy, and clearer disclosure of them is required to reassure voters that Mrs. Clinton’s candidacy is unencumbered by hidden entanglements.

In the same spirit, the Clintons are obliged to make prompt disclosure of the major donors who have been backing the former president’s library and foundation. It is not even clear whether Mr. Clinton would disclose his library’s donors if his wife won the White House.