Filtration or centrifugation are two methods frequently used to clarify human whole saliva. This study compares both the drop in peroxidase activity following filtration (49.3% +/- 16.4%; N = 12) or centrifugation (33.6% +/- 15.9%; N = 6) and the drop in total protein concentration after filtration (33.9% +/- 13.4%) and centrifugation (23.6% +/- 8.7%). After filtration, the loss was not only due to retention of the large particle-bound fraction but also to adsorption on the filter membranes. This adsorption could be inhibited by a previous dilution of saliva in a citrate buffer, which also gave rise to active subunits with a molecular weight less than or equal to 100 kDa.