A quartet of leading Wall Street banks have unleashed more than 800 new Sell ratings on US-listed companies as they usher in new equity ratings. The surge of downgrades represents a 25-fold increase in Sell recommendations from the four firms in just over one month.

Credit Suisse First Boston, Salomon Smith Barney, Lehman Brothers and Bear Stearns had Sell or underperform ratings on 34 stocks in August. That has sky-rocketed to 833 as new ratings systems have come in, according to data from Thomson Financial's First Call.