Background and Design.- Data on the prevalance of H. influenzae infections in Turkey are insufficient and usually, the treatment is empiric dur¬ing acute exacerbations in patfents with chronic obstructive pulmonary disease (COPD). We investi¬gated the effect of H.influenzae in this group of patients. Microbiological examination of sputum was made in 20 patients (18 males, 2 females) with COPD who were admitted to our clinic with an acute infec¬tion. Results.- Only one pathogenic agent was deter¬mined in 32% of patients and more than one in 37%. H. influenzae was detected in 40% of the cases, while Enterobacter spp. was found in 20%, B. catarrhalis in 15%, S. pneumoniae in 10%, E. coli in 10%, H. parainfluenzae in 5% and P. aeruginosa in 0.5%. Conclusion.- We conclude that H. influenzae is one of the most important pathogens causing acute infection in COPD patients.