Regulators are examining whether Morgan Stanley, the investment bank that shepherded Facebook through its highly publicized stock offering last week, selectively informed clients of an analyst's negative report about the company before the stock started trading.

Rick Ketchum, the head of the Financial Industry Regulatory Authority, the self-policing body for the securities industry, said Tuesday that the question is "a matter of regulatory concern" for his organization and the Securities and Exchange Commission.

The top securities regulator for Massachusetts, William Galvin, said he had subpoenaed Morgan Stanley. Galvin said his office is investigating whether Morgan Stanley divulged to only some clients that one of its analysts had cut his revenue estimates for Facebook before the stock hit the market on Friday.

The bank said late Tuesday that it "followed the same procedures for the Facebook offering that it follows for all IPOs," referring to initial public offerings of stock. It said that its procedures complied with regulations.

The questions about the role played by Morgan Stanley, the lead underwriter for the deal, add to the confusion surrounding Facebook's IPO. In the most hotly anticipated stock debut in years, the offering raised $16 billion for the social networking company, valuing it at $104 billion.