Prosecutors said Wednesday they are dropping most of the charges against the Boston University students who allegedly left five stripped-down fraternity pledges covered with condiments in a hazing incident in April.

Two of the nine defendants, Jesse Kay, 20, and Spencer Davidson, 21, still face the most serious charge of assault and battery for what prosecutors have described as inhumane treatment of the pledges, found by police shivering in the basement of an Allston home that was being used as the Alpha Epsilon Pi house. Both men, who appeared to be the ringleaders in the hazing ritual, also face single counts of hazing and failure to report hazing.