Ten patients with infections (8 neonates and 2 infants) were treated with 10.2 mg/10.2 mg/kg-37.7 mg/37.7 mg/kg of imipenem/cilastatin sodium (IPM/CS) b.i.d. or t.i.d. by a 1-hour intravenous drip infusion. The plasma concentrations of IPM/CS were determined in 5 of the 10 patients and in the cerebrospinal fluid of 1 patient of the 5. 1. The patients studied included 5 with pneumonia and 1 each with urinary tract infection, omphalitis, suspected meningitis, periproctal abscess and suspected septicemia. Clinical efficacy was evaluated in 9 patients: the patient with suspected meningitis was excluded from the clinical evaluation because the infection was doubtfully due to bacteria. Responses were excellent in 4 and good in 5 patients. No patient with a poor response was observed. All of the 6 etiological isolates obtained from 5 patients (2 strains of Staphylococcus aureus and 1 each of Escherichia coli, Enterococcus faecalis, Streptococcus agalactiae and Bacteroides fragilis) were eradicated. 2. As for side effects, rash was observed in 1 patient and petechiae accompanied by decreases in platelets and reticulocytes and increases in GOT and GPT were observed in another. Other abnormal laboratory test values in addition to the above abnormalities consisted of an increase in GPT in 1 patient and increases in GOT and GPT in another. These side effects and abnormalities in laboratory test values were mild and normalized after discontinuation or completion of IPM/CS administration.(ABSTRACT TRUNCATED AT 250 WORDS)