A biological bank has been developed to extend the biochemical and molecular research base for a prospective study on diet and cancer in the city of Malmo, Sweden. The study entered individuals 45-69 years of age, of which 30,382 individuals (45%) participated. Each individual entering the bank has stored samples of viable mononuclear leukocytes (MNLs; -140 degrees C) and granulocytes (GRANs; -80 degrees C) or buffy coats (-140 degrees C), erythrocytes (-80 degrees C), and plasma/serum (-80 degrees C). The bioassays developed to monitor the quality of storage conditions were: (a) viability and growth response to phytohemagglutinin for MNLs; (b) DNA strand breakage for GRANs; (c) NAD content for erythrocytes; and (d) thiol status for plasma/serum. The yield, purity, and storage conditions were all quality controlled, and the samples were determined to be of high standard after 137-190 weeks of storage. No differences in yield and purity were found in samples banked by different laboratory technicians. Growth responses of MNLs were severely reduced (90%) after 40 weeks of storage, which justified switching from the storage of purified MNLs and GRANs to the more cost-effective banking of buffy coats. We conclude that the quality of the banked material, based on the biochemical analysis done, indicate that the storage conditions are optimal at least up to 3.5 years, except for the growth response of MNLs.