Objective: The most important mechanism of beta-lactam resistance in gram-negative bacilli is the inactivation of antibiotics by beta-lactam enzymes. Among these beta-lactam enzymes, plasmidic AmpC type beta-lactamases have a special place as a consequence of the following reasons: they have a broad substrate profile including cephamycins, the resistance created by them cannot be inhibited by the beta-lactamase inhibitors; they can spread a multiple antibiotic resistance among bacteria and finally there are no standard recommended methods for their detection. In this study, we have examined the availability of plasmidic AmpC type beta-lactamases among Escherichia coli and Klebsiella pneumoniae strains in our laboratory. Material and Methods: Twenty three Escherichia coli and 17 Klebsiella pneumoniae strains resistant or intermediately resistant to cefoxitin isolated from the various clinical samples in Cerrahpasa Faculty of Medicine Department of Clinical Microbiology Laboratories between January 2008-September 2008 were examined. Gene areas of AmpC type beta-lactamases were investigated with polymerase chain reaction (PCR) method by utilization of appropriate primer sequences. Results: As a result, a CMY-2 gene was screened in one E. coli strain. Strain detected to be positive by PCR, was also found to be positive by phenotypic methods such as cloxacilline inhibition and modified Hodge tests. Conclusion: AmpC beta-lactamases appear to be increasing in prevalence around the world, can cause nosocomial outbreaks, and merit further study to define the best options for detection and treatment.