The effects of lomefloxacin on the in-vitro ERG were studied in the rabbit. The ERG was unchanged during perfusion with 100 microM lomefloxacin. The oscillatory potential was selectively diminished with 300 microM lomefloxacin. The suppressive effect of 300 microM lomefloxacin on the oscillatory potential was antagonized by 0.2 microM bicuculline or 0.2 microM picrotoxin. Bicuculline (0.2 microM) or picrotoxin (0.2 microM) antagonized the suppressive effect of GABA (50 microM) on the oscillatory potential. Bicuculline (1.0 microM) alone, picrotoxin (1.0 microM) alone or GABA (50 microM) alone did not augment the oscillatory potential. The findings of the present study suggested that lomefloxacin, a new quinolone agent, inhibits GABA receptor binding in the rabbit retina.