The detection of sulfhydryl groups in proteins is limited by the inacc
essibility of the sulfhydryls to the reagent, 5,5'-dithiobis(2-nitrobe
nzoic acid). The addition of other disulfides such as 2,2'-dithiobis(e
thylamine) to the chromophoric disulfide increases both the rate and t
he extent of detection of ''buried'' sulfhydryl groups in proteins.