Susceptibility of 340 mainly clinically isolated Gram-negative non-fermenters to ciprofloxacin, norfloxacin, amifloxacin, pefloxacin and cefpirome was determined by agar dilution. Ciprofloxacin was most active, with MIC90s against all organisms ranging between less than 0.125 and 4 mg/l. Norfloxacin, amifloxacin and pefloxacin were active against most strains, with MIC90 ranges (mg/l) of 0.5 - 32, 0.25 - 32 and less than 0.125 - 16, respectively. Cefpirome showed less activity than the quinolones on a weight-for-weight basis with MIC90s ranging from 0.5 to greater than 64 mg/l; only fluorescent pseudomonads and Acinetobacter calcoaceticus biotypes haemolyticus, alcaligenes were uniformly susceptible to cefpirome. The broad-spectrum activity of the four quinolones suggests potential use in therapy of infections caused by non-fermenters; cefpirome should be reserved for infections caused by fluorescent pseudomonads and possibly Acinetobacter spp.