SummaryIn a multicenter study the susceptibility of 1784 strains isolated from urine and of 700 strains from other clinical specimens has been tested to norfloxacin in comparison with nalidixic acid and different other antibiotics. Full susceptibility or partial susceptibility to norfloxacin was found in 99 % of the 1959Enterobacteriaceae, in 97% of the 334Pseudomonas, in 100% of the 219 staphylococci and in 94 % of the 100 enterococci. The large majority of strains resistant to nalidixic acid remained susceptible to norfloxacin.