A total of 94 clinical strains as well as two standard strains of Pseudomonas aeruginosa were tested for their susceptibility against 11/3-lactam antibiotics. All isolates were resistant to at least 6 antibiotics including: ampicillin, amoxycillin, amoxycillin/clavulanic acid, cephalexin, cephaloridine and cioxacillin. Ceftazidime , aztreonam and/or imipenem, exhibited the highest activity with resistance rates of 2.1% and 3.1% respectively, followed by cefotaxime (14.6%) and ceftriaxone (38.5%). Isolates no. 88 and 90 were resistant to all antibiotics under investigation except imipenem. The resistant patterns of P. aeruginosa isolates were heterogenous, since as many as 8 different patterns were recognized among the tested isolates, fi-lactamases from twelve mostly resistant isolates of P. aeruginosa were analyzed by isoelectric focusing(IEF). Six isolates from the twelve multiresistant P. aeruginosa isolates revealed the same pattern of /3-lactamases with isoelectric focusing point ranging from 7.5-8. 7. However, the highest production of (3-lactamases were detected in isolates no. 33, 90 and'94, these isolates revealed different resistant patterns. The same multiresistant isolates used in isoelectric focusing were screened for their plasmid profiles. The results indicated that P. aeruginosa isolates with the same plasmidprofiles showed different resistant patterns.