Abstract: A method for preparation of immunoglobulin fragments by specific fragmentation of immunoglobulins, comprising treating a solution of immunoglobulins with a soluble protease so as to achieve substantially complete fragmentation of the immunoglobulins, followed by complexing the protease with a complexing agent (for example, antibody to the protease) to form a protease complex and separating the protease complex from the immunoglobulin fragments. Optionally, the protease (e.g., pepsin or papain) is inactivated prior to formation of the protease complex. In contrast to methods which use immobilized forms of the enzymes, the rate of cleavage and the final yields of F.sub.(ab) and F.sub.(ab')2 fragments are increased substantially.