Examinations were undertaken to compare the results of disc diffusion tests applied for detection of strains producing extended-spectrum beta-lactamases (ESBLs). A total of 120 clinical strains were used in experiments. These strains were determined as ESBL-positive on the basis of consistent results of two methods: the double disc synergy test (DDST) according to Jarlier et al. (1988) and the diagnostic disc test (DD, version CPD/CD 01) according to Appleton (1999). In the next step examined strains were analysed in two further tests, which are variants of DD method: CAZ/CD 02 test with discs containing ceftazidime and ceftazidime/clavulanic acid, and CTX/CD 03 test with the use of cefotaxime and cefotaxime/clavulanic acid discs. ESBL-positive strains first of all belonged to the species E. coli and K. pneumoniae. In the case of seven analysed strains consistent results of determinations were not obtained with the use of different disc diffusion methods. Application of several disc diffusion methods to determine ESBL-positive strains of gram-negative rods increases the probability of their proper identification.