The CTX-M-15 extended-spectrum beta-lactamase (ESBL) was recently identified in Enterobacteriaceae isolates in India, and demonstrated significant hydrolytic activity against ceftazidime, in contrast to the majority of CTX-M enzymes. CTX-M-15 differs from CTX-M-3, which is one of the most prevalent ESBLs in Poland, by only a single amino acid change (Asp-240-->Gly). Three cefotaxime- and ceftazidime-resistant Enterobacteriaceae isolates, recovered during 1998-2000 in two Polish hospitals, were found to produce CTX-M-15. Similar to those from India, the isolates contained the ISEcp1 insertion sequence located upstream of the bla(CTX-M-15) gene, which has been recently demonstrated to mobilize 3'-adjacent genes to transfer between DNA replicons. However, its different position with respect to the beta-lactamase gene indicated the independent selection of the ESBL gene in the two countries.