Summary 1. Chloromycetin acid succinate in a doseof 25 mg. per kilogram per day appears to be insufficient to maintain effective blood levels in premature infants if given intramuscularly in divided doses every 8 hours. 2. Chloromycetin acid succinate, 25 mg.per kilogram per day, given in a single dose intramuscularly produces effective blood levels within 3 hours which persist for at least 9 hours in premature infants, but only rarely for 21 hours in infants over 6 days of age. 3. A good method of administering chloramphenicolto newly born premature infants to maintain an effective and not unduly high blood level is with a dose of 25 mg. per kilogram Chloromycetin acid succinate and 25 mg. per kilogram of Chloromycetin intramuscular given intramuscularly in separate syringes; these administrations are repeated in 48 hours. None of the infants thus treated in the present study manifested toxic symptoms. 4. Premature infants over 4 days of agemay require the same dosage every 24 to 36 hours to maintain similar levels. Further study will be necessary to confirm this assumption, however.