We compared 40 patients taking lomefloxacin 400 mg once daily for 5 days in a double blind trial with 44 placebo takers with proven community acquired bacterial diarrhoea (85% due to Campylobacter spp.). Lomefloxacin eradicated Campylobacter spp. in 75% but did not alter clinical outcome. Twenty-eight per cent of the campylobacter isolates developed resistance. Thirty-three per cent developed side-effects. Lomefloxacin is not recommended for community-acquired bacterial diarrhoea when Campylobacter spp. predominate.