In order to measure the plasma levels of interleukin-4 (IL-4). cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in patients with chronic obstructive pulmonary disease (COPD) and observe the effects of oral theophylline on them, we divided 28 COPD patients into COPD experimental group and COPD control group. Plasma levels of IL-4, cAMP and cGMP as well as parameters of pulmonary function tests were measured in these 2 groups before and after 2 weeks of treatment with oral theophylline (Protheo, 400 mg, qd) or placebo. Plasma levels of IL-4 and cGMP were significantly elevated in patients with COPD as compared with normal controls (P< 0. 05), while cAMP and cAMP/cGMP were significantly lower than those in controls (P < 0. 01). Plasma level of IL-4 was inversely correlated with forced expiratory volume at the first second (FEV₁) and with maximum expiratory flow rate at 50 % of forced vital capacity (V₅₀) (bothr= −0.46,P< 0.05) while it was directly correlated with the scores of the clinical manifestations (r=0.57,P< 0.05) in COPD patients. Two weeks after treatment with theophylline, IL-4 and cGMP in COPD experimental group were decreased significantly while cAMP and cAMP/ cGMP increased significantly (P< 0. 05). The change of IL-4 was inversely correlated with the changes of FEV₁, and V₅₀(r=−0.53 and -0.54, respectively,P< 0. 05). Two weeks after placebo treatment, the COPD control group did not show such changes. We are led to conclude that IL-4 might play a role in the pathogenesis of the airway inflammation and air flow limitation in COPD patients and the mechanisms of theophylline’s therapeutic efrects of attenuating air-flow limitation may partially depend on its anti-inflammatory effects on the airways which, in turn, is dependent on its inhibitory effects on some inflammatory mediators such as IL-4.