Brief exposure of serum to alkali in the cold seems to convert non-precipitating antibody to a precipitin-like material. This was disclosed by the following lines of evidence.
1. Immune sera, after addition of antigen and removal of the ensuing precipitates, yielded after alkali treatment more antibody-antigen complex than did sera to which no antigen was added.
2. When immune sera were depleted of precipitating antibody, treated by alkali, and antibody-antigen complex was allowed to precipitate, the resulting supernates formed additional prescipitates upon admixture of specific antigen. No precipitation occurred upon addition of non-specific protein to the treated supemates or the addition of specific antigen to depleted sera not treated by alkali.
3. Alkali-treated immune sera precipitated more antigen than untreated sera.