Seven antibiotics, such as gentamycin, kanamycin, streptomycin, polymyxin M, carbenicillin, tetracycline and rifampicin were studied with respect to their effect on 260 strains of Ps. aeruginosa isolated from various sources within 1945-1971. Gentamycin and polymyxin M proved to be most active in vitro. Carbenicillin showed moderate activity. The sensitivity levels of the cultures of Ps. aeruginosa isolated from various sources within 30 years were identical. Serological typing of 59 cultures of Ps. aeruginosa was performed and their virulence was studied in parallel with their antibiotic sensitivity testing. No correlation between the antibiograms, serotypes and virulence of Ps. aeruginosa was found.