The prothrombotic state frequently observed in patients with chronic obstructive pulmonary disease (COPD) may be related to a systemic inflammatory response. In the present study plasma interleukin-6 (IL-6), IL-2 and IL-1beta levels have been investigated in 33 patients with COPD. In vitro platelet activity, plasma C-reactive protein (CRP) and fibrinogen levels were also determined in all patients. The results obtained demonstrated that plasma IL-6 levels were significantly higher in the patient group compared with a control population age and sex-matched ( P < 0.02), while plasma IL-2 and IL-1beta levels were not significantly modified. An overall condition of platelet hyperactivity in COPD patients was also observed. A comparative analysis of platelet activity and blood gas levels demonstrated a correlation between platelet hyperactivity and a severe impairment of oxygen ( P < 0.001) and carbon dioxide tensions ( P < 0.01). Finally, a statistical analysis of the population under study showed the presence of a significant correlation between elevated plasma IL-6 ( P < 0.001) and IL-1beta levels ( P < 0.007), and an increased sensitivity of platelets to arachidonic acid, suggesting a possible correlation between the inflammatory response and the prothrombotic state observed in patients with COPD.