Since previous work has not adequately addressed temporal variation in the oral microbiome, we propose to: 1) establish a cohort of 40 adults willing to provide oral samples approximately every two months for one year; 2) process all oral samples and evaluate the presence and quantity of microbiota using 16S ribosomal RNA gene sequencing; 3) calculate appropriate reliability measures for the sample over time using the intra-class correlation coefficient (ICC) for and <= diversity metrics; and 4) empirically evaluate the efficiency of different longitudinal designs including two or more sample collections with an outcome such as body mass index (BMI). Because of the complexity and high prevalence of human DNA in saliva, metagenomic analyses of oral samples are not yet feasible, however, the samples obtained from this study will be available for use in future metagenomic analyses when the technology is operationalized. The current study is essential to establish the reliability of a single measure of the oral microbiome to determine appropriate sample sizes for future cohort studies considering the effect of the oral microbiome on the risk of cancer and other health outcomes.