The aim of this study was to determine the types of beta-lactamases by isoelectric focusing in the 56 ESBL producing Klebsiella strains isolated in our hospital between January 2002-December 2004. The presence of more than one enzyme (62.5%) was observed by isoelectric focusing in the majority of the analysed bacteria. The most commonly designated pI points for the enzymes obtained from both Klebsiella species were 7.6, 7.2 and 8.4. Consecutive pI points were 8.6, 8.2, 5.6, 7.0, 7.8, 8.0, 5.4, 8.3, 8.8, 9.0, 5.9 and 6.8 in order of frequency. With regard to the isoelectric points determined in the strains, the anticipated SHV enzyme types were SHV-3, SHV-3-like enzymes (pI 7.0), SHV-4, SHV-4-like enzymes (pI 7.8) and the CTX-M type enzymes were CTX-M-15 (pI 8.6), CTX-M-20 (pI 8.3) and CTX-M-5 (pI 8.8). The isoelectric points 5.4, 5.6 and 5.9 were determined with concordance to the TEM group enzymes. It is concluded that SHV and CTX-M enzymes were the most common enzymes among the bacteria analysed.