OBJECTIVE: To compare peripheral T lymphocyte apoptosis of chronic bronchitis during an acute episode with that during a stable period. METHODS: Seventeen Chronic Btonchitis patients who presented to the ER with an acute episode were compared with 10 stable Chronic Bronchitis patients seen in the out-patient clinic. Peripheral venous blood was obtained from each patient and T lymphocytes were separated by fluorescent monoclonal antibodies. CD3, CD95 and CD25 were measured by flow cytometry. RESULTS: In the acute episode patients, the total quantity of T lymphocytes with CD3 was (42.63 +/-16.37) and with CD95 (14.15 +/-11.06). In the stable group T lymphocyte CD3 was (64.22 +/-23.90) and CD95 (34.88 +/-8.92) (t=-4.238, P <0.001; t=-8.796, P <0.001). The total quantity of Lymphocyte CD25 did not differ significantly between the two groups (P > 0.05). Total quantity of active T lymphocytes with CD3/CD25 was lower in the acute episode group (6.26 +/-3.94) compared to the stable group (10.52 +/-3143) (t=-1.068, P <0.05). CONCLUSION: T lymphocyte apoptosis increased in Chronic Bronchitis patients who presented with an acute episode. They also experienced a significant disturbance in immune function.