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Gene expression profiling is increasingly important in human health research and applications (1). Unfortunately, the human tissue samples required for this process, particularly those from healthy individuals, are not safely and easily available. Therefore, the use of peripheral blood mononuclear cells (PBMCs) as surrogate material for high-throughput analysis of gene expression is currently being explored. These cells are involved in a large variety of immune-related diseases, including infection and cancer. Moreover, in recent studies, characteristic sets of transcriptional changes in PBMCs were associated with physiologic or pathologic states (2)(3)(4). Thus, a PBMC transcriptome may be used as an individual’s health sensor, a concept referred to as the sentinel principle (5). In large multicenter studies, the reliable and reproducible detection of transcript concentrations from PBMCs requires standardization of blood sampling and an efficient method of conservation. Indeed, many preanalytical factors during collection, processing, and storage of blood specimens may affect RNA and its subsequent use as a biomarker (6). Although numerous technical and clinical aspects of blood sampling have been addressed (7)(8)(9), comprehensive data on the long-term storage and stability of RNA from PBMCs are needed. Here we report experiments performed over 15 months to test the preanalytical conditions involved in blood collection procedures and PBMC storage. Blood samples were collected from healthy donors into EDTA and sodium heparin tubes. RNA extractions were performed on isolated PBMCs stored at −80 °C up to 15 months in 4 different lysis buffers. Using spectrometry and real-time PCR, we compared the concentration, purity, integrity, and stability of the total RNA. We propose a quality-assured and controlled protocol of PBMC banking for further mRNA expression analysis. After informed consent was obtained from 12 unrelated adult volunteers, whole blood (10 mL) was collected by standardized venipuncture in …