Salivary F has often been used as a measure of the efficacy of topical F agents. Based on physiochemical considerations, the relevant factor in such measurements is the free F concentration. Unfortunately, many authors report the total salivary F, which can include a substantial contribution from F-containing particles. Objectives: To determine if changes in total salivary F can be used to estimate changes in salivary free F. Methods: Two studies were performed in which 12 subjects fasted overnight, followed by a morning 228 ppm NaF rinse (Study 1), or a 150 mmol/L calcium lactate pre-rinse immediately followed by the F rinse (Study 2). One h later saliva samples were collected. Whole, vortexed saliva was made 1 M in percholoric acid, digested overnight, neutralized and TISAB diluted for determination of total F. The remaining saliva was immediately centrifuged and TISAB diluted for determination of free salivary F concentration. All samples were analyzed using an inverted electrode method. Results: The data was log transformed and hence data is presented as geometric mean (µmol/L) and standard error factor {SEF}. Study 1 (NaF rinse): Total saliva F=67{1.7}; centrifuged saliva 18{2.5}. Study 2 (Ca pre-rinse/NaF rinse): Total saliva F=1029{2.5}; centrifuged saliva 68{2.3}. Statistical differences were determined using a one-way ANOVA followed by an all pairwise multiple comparison procedure. Conclusions: As in previous studies, the Ca pre-rinse greatly increased (p<0.05) total and centrifuged saliva F. In both studies total saliva was much greater than centrifuged saliva (p<0.05). However, the Ca pre-rinse increased total saliva F by 15.3x while centrifuge saliva F increased only 3.8x. Thus, in agreement with previous studies using other experimental rinse procedures, changes in total salvia F greatly exceeded changes in centrifuged/free salivary F. Hence, centrifuged salvia F measurements should be used to predict topical F efficacy. Supported by the ADAF and NIST.