Aside from its function as the "blueprint of life" that encodes genetic information, DNA can have direct immune activities. The immune system has evolved a defense mechanism that is able to distinguish microbial DNA from our own because of differences in the frequency and methylation of CpG dinucleotides in particular base contexts. Within minutes of detecting such "CpG-S DNA," cells of the innate immune system become activated and produce cytokines that promote the generation of antigen specific T-helper-1-like immune responses. Animal studies indicate therapeutic utility for CpG-S DNA as a vaccine adjuvant and for the immunotherapy of cancer and infectious and allergic diseases.