Gentamicin (GM) was intramuscularly injected to 16 children with various infectious disease (1 septicemia, 1 purulent meningitis, 4 bronchopneumonia, 1 pyothorax, 3 pyelonephritis, 2 acute cystitis and 4 RITTER'S dermatitis). The results obtained are as follows: 1. The excellent and good clinical results were noted in all patients except for an indeterminate case with bronchopneumonia because of the concomitant therapy with CEZ. The effective rate was 100.0%. This was possibly because of quite high susceptibility (See Article) of all isolates to gentamicin. 2. Doses of GM were adjusted depending on the style of infectious diseases. The satisfactory clinical results were obtained in some cases by increasing its recommended dosage to about 5-8 mg per kg per day. 3. No kidney dysfunction, liver dysfunction, the 8th cranial nerve damage, etc. were observed by administering 5 to 8 mg per kg per day for at maximum 18 days, in this clinical trial. 4. It has been indicated in this clinical trial that GM is worthy to be used as a first-choice drug in chemotherapy of infectious diseases caused by Staphylococcus, gram-negative bacillus, etc., especially in patients who are hypersensitive to penicillin and cephalosporin derivatives. However, further study would be required for the safety of increase in its dosage and duration of administration.