Cohort studies commonly store blood samples to measure the associations of biomarkers with disease risks for a long time after the study subjects are enrolled. To obtain valid measurements of the stored samples, monitoring their degree of deterioration is essential. The first stage of the Japan Multi-Institutional Collaborative Cohort (J-MICC) Study launched in 2005 included a project to validate the quality of stored blood samples. This project will compare the measurements of representative molecules over different storage periods (1, 4, and 8 years after sampling, and when a nested case-control study is conducted), different storage temperatures (-80 and -150 degrees C), and different separation conditions (temperature and time) before storage. For these purposes, 28 ml of peripheral blood from 10 people was sampled four times annually, using two tubes for serum and two EDTA-Na tubes for plasma. These samples were treated using the process adopted for the J-MICC study protocol, and stored in tubes containing 300 microliters of serum or plasma labeled with two-dimensional bar codes. The sampling was started in 2006, and some of the specimens will be stored until the end of the J-MICC Study in 2035. The resulting findings will produce valuable information on the stability of the molecules, not only for the J-MICC Study, but also for other cohort studies.