Twelve dogs were referred with purulent and proliferative otitis externa. Prior treatment included fluoroquinolones, glucocorticoids and polyvalent ear drops over seven days to five months. In all cases the vertical and horizontal ear canals were inflamed and thickened, with ruptured tympanic membranes in four cases. No abnormalities were seen on radiography of the osseous bullae. Numerous rod bacilli and degenerate neutrophils were seen on cytology. Pseudomonas aeruginosa resistant to fluoroquinolones and gentamicin was cultured in all cases. Treatment was initiated with 1 to 2 mg/kg prednisolone per os once daily, and a cleansing and drying ear cleaner followed by topical administration of injectable ticarcillin solution four times daily. Cases with ruptured tympanae also received 15 to 25 mg/kg ticarcillin three times daily intravenously until the membranes had healed. All cases were anaesthetised for repeated saline ear flushes until no further discharge was evident and no rods were seen on cytology. Topical ticarcillin and the ear cleaner were continued twice daily for 14 days after clinical resolution. The duration of treatment ranged from 14 to 36 days. Treatment was withdrawn in one case which developed a drug reaction. All other cases responded well with no adverse effects.