17 cases of purulent meningitis in 15 children, aged 1 day to 5 years (median 8 months) were treated with continuous i.v. infusion of chloramphenicol succinate. Free chloramphenicol in serum and cerebrospinal fluid (C.F.) was assayed by high performance liquid chromatography (HPLC). CF chloramphenicol levels averaged 45 +/- 14% of the serum level. Out of 16 patients only five received the usually recommended dosage. In three others because of initially or progressively high serum levels the dose had to be diminished. In eight others because of subtherapeutic levels the dose had to be raised. The highest dose (390 mg/kg body weight/d) was required in a 2 month old boy. He was shown to have a clearance rate for free chloramphenicol considerably higher than has been reported so far. Maturation of the metabolism could be observed in a small-for-date newborn who acquired a grey baby syndrome during the treatment of his first meningitis. Several weeks later he required exactly the recommended dose to reach therapeutic chloramphenicol levels. As a consequence of these observations we strongly recommend meticulous drug monitoring of chloramphenicol in order to meet the large biological variations seen particularly in neonates and young infants in their capacity to reach and maintain therapeutic serum levels.