Pseudomonas aeruginosa is an important opportunistic pathogen. P. aeruginosa strains secrete several virulence factors, in the form of extracellular proteins. Adhesins, pyocyanin, proteases, hemolysins, exotoxin A and exoenzyme S are some of the virulence factors found in P. aeruginosa strains. In this study, the presence of siderophore, total matrix protease and elastase activities were investigated in a total of 157 P. aeruginosa strains isolated from lower respiratory tract (n: 81; sputum, bronchoalveolar lavage, tracheal aspirate) and extrarespiratory sites (n: 76; urine, wound, blood) of hospitalized pati ents. Chrome azurol S (CAS) agar plates were used for detection of siderophore activity. Hide powder azure was used for the investigation of total matrix protease activity and elastin congo red was used to test elastase activity. All strains gave positive reaction on CAS agar. Enzyme activities of the test strains were compared with the activity of P. aeruginosa PAO1 positive control strain. Mean total matrix protease and elastase activities were less than P. aeruginosa PAO1 activity in the test strains, however, some strains exhibited activity higher than PAO1. There was no significant difference for mean protease and elastase activities between the strains isolated from lower respiratory tract samples and the others (p > 0.05) [corrected] as well as no difference with respect to antibiotic resistance (p > 0.05) [corrected] It was found that ceftazidime and cefoperazone were the most resistant agents in both groups (67.9% and 57.9% for ceftazidime and 49.3% and 48.7% for cefoperazone, respectively). It was concluded that further in vivo studies are necessary to clarify the role of virulence factors of P. aeruginosa in the establishment of infection in different body sites.