The colony hybridization and tetracycline accumulation techniques made possible to demonstrate the majority of the 29 bacteria of Pseudomonas genera to harbour the plasmids carrying tet determinants belonging to classes A-C, while one strain contained a plasmid carrying tet determinant of class B. For the first time the determinants of classes D and E were found on R plasmids in Pseudomonas aeruginosa. The determinant of G class was identified on two plasmids identical to pBS221 plasmid described previously.