The treatment of patients with asthma that is resistant to corticosteroids represents a therapeutic challenge, because corticosteroids are the most potent and potentially effective medications for severe asthma. Recent investigations have identified several functional defects in mononuclear cells and T lymphocytes isolated from patients with corticosteroid-resistant asthma, including abnormalities in proliferation, activation, and cytokine production. The development of medications with immunomodulatory effects on specific cellular functions represents an exciting step for more efficacious treatment for such patients.