Studies have shown that a concentrated calcium (Ca) pre-rinse given before a fluoride (F) rinse or dentifrice greatly increased the one-hour post application salivary and plaque fluid F [IADR 2005, ORCA 2005].  Objectives:  To determine the effect of a Ca pre-rinse/NaF rinse on the amount of F that can be extracted by neutral or acidic buffers from human plaque. Methods: 13 subjects rinsed 1 min with 20 ml of 150 mM Ca lactate and then rinsed 1 min with 20 ml of a 228 ppm F NaF rinse.  A no pre-rinse/NaF rinse served as the control. One h post-rinsing, 2 plaque samples were collected and sequentially extracted 5 times (1 h each extraction) with pH 6.8 PIPES or pH 4.8 acetate buffer.  The remaining F was then determined by acid extraction.  The extracts (15 ml/mg for extraction 1, 45 ml/mg for extractions 2-5 and the acid extraction) were analyzed for F [Vogel et. al., Caries Res. 2001;35:116]. Results: For the Ca pre-rinse/NaF rinse the F (mg) extracted per g of plaque by the 5 sequential pH 6.8 extractions were (± = standard error): 58±13, 88±11, 61±11, 55±10, and 44±8.  The corresponding values for the NaF rinse were: 3.0±0.4, 4.7±0.8, 3.4±0.6, 3.2±0.5, and 2.9±0.6.  For the pH 4.8 extracts the Ca pre-rinse/NaF rinse results were: 81±11, 124±15, 80±13, 52±9, 37±8 and for NaF 12.8±3.1, 20.7±5.0, 12.3±4.3, 5.4±2.3, 1.5±0.6.  The average total F in the two plaque samples was 452±50 for Ca pre-rinse/NaF rinse and 47±7 for the NaF rinse alone. Conclusion: A 150 mM Ca pre-rinse before a NaF rinse greatly increased the amount of exactable F in plaque (p<0.05, paired diff. test).  Supported by NIDCR grant DE05354, ADAF, and NIST.