Chickens 14 days old were experimentally inoculated with Mycoplasma gallisepticum (MG) R-P10 strain. After development of respiratory symptoms, birds were left unmedicated or medicated for 5 consecutive days with Difloxacin 5, 7.5 or 10 mg/kg body weight per day or Enrofloxacin at the dose level of 10 mg/kg body weight per day. Evaluation of efficacy was based on body weight, symptoms, post-mortem findings, re-isolation of MG and serology. Results indicated that under the conditions of this experiment, treatment with 7.5 mg Difloxacin per kg body weight for 5 days was already effective against pathogenic MG infection. The dose of 10 mg/kg Difloxacin was equally effective as a dose of 10 mg/kg Enrofloxacin in treating respiratory symptoms.