The aim of the investigation was to determine the properties of SHV-2 type of beta-lactamase from two hospitals in Zagreb. The production of SHV-2 beta-lactamase was determined in 22 clinical isolates of K. pneumoniae by isoelectric focusing, PCR and PCR/Nhe test. The organisms were collected from the Sestre Milosrdnice Hospital and Dubrava Hospital in Zagreb during 1994-1995. Nine out of 22 strains transferred resistance to E. coli recipient. In spite of the fact that SHV-2 beta-lactamase is a cefotaximase, only 18% of the strains were resistant to cefotaxime with standard inoculum size but the percentage of resistant strains rose to 39% when the inoculum size was increased to 10(7) CFU/ml. The frequency of transfer was lower when more stringent conditions were applied (higher concentration of cefotaxime in the medium) but the transconjugants obtained with such conditions, displayed higher level of resistance to third generation cephalosporins. The genes responsible for resistance to aminoglycosides were usually transferred on the same plasmid with the genes encoding ESBLs. All strains produced an enzyme with the isoelectric point of 7.6, yielded an amplicon with SHV specific primers and had positive PCR/Nhe test.