We describe a phenomenon of mobilization of antibiotic resistance from non-transferring strains of Pseudomonas aeruginosa by cultivation with strains of P.aeruginosa capable of transferring determinants of antibiotic resistance to a susceptible recipient strain by triparental cross. In this report we described two strains of P.aeruginosa capable to mobilize for transfer the resistance determinants in strains of P.aeruginosa with multiply antibiotic resistance which were not themselves transferable to Pseudomonas recipient strains. Two strains of P.aeruginosa No. 282 and 283 from Bata's Hospital in Zlín, Czech Republic, were used as donor strains for experiments in triparental crosses. They were resistant to carbenicillin (CAR), kanamycin (KAN), cefalotin-cefazolin (CFR), cefotaxime (CTX), ceftazidime (CAZ) and aztreonam (AZA). Both strains transferred CFR resistance to Escherichia coli K-12 rif+ recipient, but not to P.aeruginosa PAO recipients. In a second system, a strain of P.aeruginosa No. 76 from Frankfurt University Clinics was used as a donor strain. It transfers CAR resistance to PAO-1670 rif+, but not to E. coli K-12 rif+. Two strains of P.aeruginosa from Frankfurt University Clinics No. 76 and 229 were used as intermediary recipient strains. They were resistant to CAR, KAN, CTX, CAZ, AZA, imipenem (IMP) and ofloxacin (OFL). Strain No. 229 did not transfer any antibiotic resistance to any of both final recipient strains. Strain No. 76 transfers, as indicated, CAR resistance determinant to PAO 1670 rif+ recipient strain. Strains of E. coli K-12 No. 3110 rif+ and P.aeruginosa PAO 1670 rif+ were used as final recipient strains.