Efficacy, safety and pharmacokinetics of meropenem (MEPM) were assessed when 1 g (40 mg/kg for some of the pediatric patients) t.i.d. was administered every 8hours to 101 adult and 6 pediatric patients with febrile neutropenia (FN) as diagnosed based on the Japanese guideline for FN treatment. The efficacy rate evaluated as antifebrile effect up to Day 4 of treatment was 40.0% (40/100) in adult and 66.7% (4/6) in pediatric patients. The antifebrile effect in adult patients was analyzed after stratifying them according to their neutrophil counts up to Day 4. Treatment with MEPM produced an antifebrile effect not only in patients with higher neutrophil counts (> or = 500/mm3) but also in those with lower counts (< 100/mm3), and the efficacy rate was comparable between the two groups: 38.2% in the < 100/mm3 group and 29.4 to 55.6% in the > or = 500/mm3 group. The bacteriological efficacy of MEPM evaluated as disappearance rate on Days 3 to 5 and Day 7 was both 100% (8/8 and 4/4, respectively). The time above minimal inhibitory concentration (% T > MIC) in the treatment interval was greater than 90% in 9 out of 10 patients for whom likely causative organism was isolated and identified after MEPM treatment or for whom causative organism emerging after treatment was isolated and identified. The incidence of adverse events was 93.1% in adult and 83.3% in pediatric patients. There were three deaths and one serious adverse event reported among the adult patients; however, all these cases were assessed as not related to the study medication. The incidence of adverse drug reactions was 45.5% and 66.7%, respectively. All the observed adverse drug reactions were mild or moderate in severity and none of them was severe. Adverse drug reactions which were unknown from the previous MEPM clinical studies and investigation of the results of clinical experience include 'chest discomfort', 'blood uric acid decreased', 'lymphocyte deformation', 'blood uric acid increased', 'abnormal funduscopy', 'hypesthesia' and 'hemorrhagic cystitis'. All these events were mild or moderate in severity and resolved without requiring any action or after providing symptomatic treatment. There was no unknown adverse drug reaction that resulted in treatment discontinuation. No nervous system disorders such as convulsion and impaired consciousness were reported. The results show that monotherapy of MEPM 1 g (or 40 mg/kg for some of the pediatric patients) t.i.d. every 8 hours was effective, and was also safe and well tolerated in adult and pediatric patients with FN. Therefore, MEPM monotherapy is expected to be useful as the initial treatment for Japanese patients with FN.