Extended spectrum beta-lactamases (ESBLs) are common in our country as well as in the world. However, data about the molecular types of these enzymes are lacking in Turkey. ESBLs were initially determined commonly as TEM and SHV derivatives, but in recent years CTX-M enzymes have become more dominant. The aim of the study was to investigate of CTX-M and PER genes in Enterobacteriaceae isolates which were positive for ESBL and carried TEM and/or SHV genes, and to determine DNA sequences of all enzymes. Presence of CTX-M and PER beta-lactamases was investigated with polymerase chain reaction (PCR) method in 28 strains obtained from the Microbiology Laboratory of Dokuz Eylul University Medical School. PCR-restriction fragment lenght polymorphism (PCR-RFLP) and DNA sequence analysis were performed on PCR positive strains. While CTX-M gene was determined in three strains using PCR, PER gene was determined in none of the strains. All CTX-M enzymes were found to belong to CTX-M-1 group according to RFLP analysis. As a result of both strands DNA sequence analysis, SHV-2 in four strains, SHV-5 in 14 strains, SHV-12 in 10 strains and CTX-M-3 in three strains were determined.