Asthma is a major health problem, of which the prevalence and severity are increasing, particularly in industrialized nations. One hypothesis for this is that diminished exposure to childhood infections in modern society has led to decreased Th1-type inflammation. Reduced Th1 responses may lead to enhanced Th2-type inflammation, important in promoting asthma and allergic disease. The most common current treatment for asthma is corticosteroids; while these agents inhibit the function of inflammatory cells, they are ineffective in altering the initial Th2-type response to allergen in a sensitized individual. A novel therapeutic approach, recently reported in the preclinical setting, is the use of oligodeoxynucleotides (ODNs), which contain unmethylated motifs centered on CG dinucleotides. These CpG ODNs potently induce Th1 cytokines and suppress Th2 cytokines, and can prevent manifestations of asthma in animal models. These agents have the potential to reverse Th2-type responses to allergens and thus restore balance to the immune system. Clinical trials are ongoing.