During different periods in 1976 and 1977 the bacteria of hospitalized patients were selected at random in significant bacteriuria. The species determination was carried out exactly and the susceptibility to beta-lactam-and aminoglycoside antibiotics was investigated using the quantitative tube dilution test. The bacterial spectrum of 941 isolated strains is shown in Table I. E. coli was found in 50% only. The spectrum of bacteria is different in the various hospitals, caused by regional phenomenons of nosocomial infections (Table II). The sex distribution (Table III) shows that mostly E. coli and Strept. faecalis are isolated from women, and Klebsiella sp. from men. The difference is significant. May be there exists a sex specificity for some bacteria. The sensitivity tests include the antibiotics Ampicillin, Carbenicillin, Ticarcillin, Mezlocillin, Azlocillin, Cefalotin, Cefamandole, Cefazolin, Gentamicin, Tobramycin and Amikazin (Table IV). Different sensitivity patterns could be established because of the exact species determination.