Minimal inhibitory concentrations (MIC) of enoxacin (ENO) were evaluated by agar dilution, in comparison with MIC of nalidixic acid (NAL), pipemidic acid (PIP), oxolinic acid (OXO), pefloxacin (PEF), norfloxacin (NOR), ofloxacin (OFL) and ciprofloxacin (CIP), for eleven Enterobacteriaceae reference strains chosen as a function of sensitivity and level of resistance to NAL. In the four strains susceptible to NAL, MIC of ENO (0.06 to 0.25 micrograms/ml) were similar to those for PEF and NOR, 2 to 4 times inferior to those for OXO, 16 to those for PIP and 32 to those for NAL; this ratio of activity was also seen in the majority of strains resistant to NAL. Measurement of MIC of ENO for 397 recent clinical isolates confirmed efficacy of this substance against Enterobacteriaceae and showed its activity against Pseudomonas aeruginosa (mode MIC: 0.5-1 micrograms/ml), and Gram positive cocci, essentially Staphylococcus aureus (mode MIC: 0.5-1). Antibacterial activity in the urine was measured by the Heilman test in 5 male adults after two doses of 200 mg of ENO administered at 12 hours intervals, two doses of 400 mg of ENO and, in comparison two of 400 mg of PIP administered under the same conditions. Maximal inhibitory dilutions obtained with ENO reached (mean for 5 subjects): 1/64 to 1/128 after 200 mg and 1/128 to 1/512 after 400 mg for a sensitive Providencia strain (MIC ENO: 0.25); 1/32 to 1/128 and 1/64 to 1/256 for an E. coli strain of low level of resistance to NAL (MIC ENO: 2); activity was very low on a Serratia strain highly resistant to NAL (MIC ENO: 16).(ABSTRACT TRUNCATED AT 250 WORDS)