Abstract A novel method for the determination of the titer of high affinity anti-trinitrophenyl antibodies has been developed. The method is based on the observation that at moderate levels of sulfite concentration ( ca. 3 × 10 −4 M) these antibodies cause the breakdown of the highly colored complexes which are formed between trinitrobenzene derivatives and sulfite anion. The method involves a rapid spectrophotometric determination and it gives titers which are in good agreement with the results obtained by more standard techniques. Preliminary kinetic experiments using the basic principles of this sulfite titration indicate the ‘off-rates’ for these anti-trinitrophenyl antibodies may be as low as ca. 10 −4 sec −1.