The efficacy of enrofloxacin against Riemerella anatipestifer (formerly Pasteurella anatipestifer) septicaemia of Muscovy and Pekin ducklings was assessed in an artificial challenge model which reproduced typical duck riemerellosis with very high mortality. Mortality, clinical signs, gross lesions, microbiological clearance, feed intake and body weight gain were the efficacy criteria studied. A pulsing medication in drinking water for 4 h at 25, 50 or 100 ppm enrofloxacin on the first day, followed by 12.5, 25 or 50 ppm, respectively, on the following 4 days, provided clinical cure of R. anatipestifer septicaemia at all dosages tested. An optimum dosage of 50 ppm enrofloxacin, followed by 25 ppm was established.