The role of the immune response in autoimmune hepatitis has not been studied before and after prednisone and azathioprine treatment. Distributions of blood lymphocytes (CD4+, CD8+, CD19+, CD23+, CD16/56+), levels of serum immunoglobulins (IgM, IgG, IgE, IgA) and cytokines (IFN-γ, IL-4, IL-12, TNFα ) were studied in a child (f/14 y/o) with autoimmune hepatitis before and after prednisone (20 mg/d) and azathioprine (50 mg/d) treatment (nephelometry, UniCAP Total IgE Fluoroenzymeimmunoassay, flow cytometry, cytokine ELISA). Patient was studied for 0-2.5 yrs; treatment was initiated 12 weeks post diagnosis. Numbers of CD4+ T cells increased (50%), while CD19+ and CD23+ cells decreased (>50%) post treatment; other lymphocyte subsets were unaffected by treatment. Serum IgG and IgE levels decreased (>50%) after treatment; serum IgM and IgA were within normal range and were not affected by treatment High levels of IFN-γ (5-23 pg/ml) were initially detected in serum, which decreased after treatment (<0.1 pg/ml). Furthermore, low levels of IL-4 (0.2 pg/mL) were detected before treatment, which were not detected after treatment (<0.1 pg/ml). In contrast, before treatment, IL-12 and TNFα were not detected in serum; however after treatment the levels of IL-12 and TNFα dramatically increased. Prednisone and azathioprine treatment decreased total serum IgG, IgE, IFN-γ and IL-4 levels, and blood CD19+ and CD23+ cells; however serum IL-12, TNFα and blood CD4+ T cells increased with treatment. Understanding immunomodulation in autoimmune hepatitis will provide better insight and mechanisms of this disease and may tailor more effective therapeutic intervention.