The appropriate administration method of levofloxacin in relation to symptoms was investigated by following up 2,353 patients prescribed either levofloxacin (300 mg divided into 3 doses) or 400 mg (divided into 2 doses) for the treatment of acute upper respiratory tract infection accompanied by fever (temperature (> or = 38 degrees C) of suspected bacterial infection. 1) The cure rate based on body temperature as an index was significantly higher in the group administered 400 mg/day compared with the group administered 300 mg/day. No significant difference between the two regimens was observed in patients with a temperature < or = 38.5 degrees C at the start of administration, but patients with a temperature > or = 38.6 degrees C showed a significantly higher cure rate when administered 400 mg/day compared with 300 mg/day. 2) No significant difference between the groups was observed with respect to the improvement of quality of life (QOL), assessed using a VAS. In patients with a temperature > or = 38.6 degrees C, however, significantly higher improvement rates were demonstrated on days 3, 5 and 6 of treatment at 400 mg/day compared with 300 mg/day. 3) The reconsultation rate was significantly lower in the group administered 400 mg/day compared with the group administered 300 mg/day. No significant difference between the groups was observed in patients with a temperature < or = 38.5 degrees C. However, in the patients with a temperature > or = 38.6 degrees C, treatment at 400 mg/day achieved a significantly lower reconsultation rate compared with 300 mg/day. 4) Nonsteroidal anti-inflammatory drugs (NSAIDs) were concomitantly administered to 64.3% of the patients, but no significant difference in the cure rate was observed between patients with or without concomitant use of NSAIDs. 5) Among all of the patients, 12.7% were positive for the influenza virus, and anti-influenza drugs were concomitantly administered to 41.3% of them. However, no significant difference in the cure rate was observed between the group administered levofloxacin alone and the group concomitantly administered anti-influenza drugs. 6) The incidence of adverse drug reactions was 0.84% in the group administered 400 mg/day and 0.50% in the group administered 300 mg/day. No significant difference was observed between these groups and no serious adverse drug reactions occurred. In conclusion, for treating patients with acute upper respiratory tract infection accompanied by fever (> or = 38.6 degrees C) and suspected bacterial infection, levofloxacin dosage of 400 mg/day (divided into 2 doses) was superior to 300 mg/day (divided into 3 doses) in terms of therapeutic effect, QOL, and the reconsultation rate. This was considered to be an administration method worth recommending, including its safety. In patients with a temperature of 38.0 degrees C to 38.5 degrees C, administration of levofloxacin at 300 mg/day was confirmed to demonstrate a sufficient therapeutic effect.