The California Public Employees' Retirement System, the nation's largest public pension fund, has invested $140 million in such unrated CDO portions, according to data Calpers provided in response to a public records request. Citigroup Inc., the largest U.S. bank, sold the tranches to Calpers.

``I have trouble understanding public pension funds' delving into equity tranches, unless they know something the market doesn't know,'' says Edward Altman, director of the Fixed Income and Credit Markets program at New York University's Salomon Center for the Study of Financial Institutions.

Is your pension fund fund buying CDO's?  Check out the Bloomberg article.