Nucleic acid and cell preservative compositions. Methods of preserving nucleic acids and/or cells in a blood or other biological sample, and kits for preserving nucleic acids and/or cells in a blood or other biological sample are also described. The preservative compositions, methods and kits afford the isolation of genomic and cell-free DNA and RNA from myriad biological samples that display good yields, purity, integrity and, in the context of RNA, amplifiability.