An intravenous preparation of doxycycline (DOTC, Vibramycin 'Pfizer'), a long-lasting tetracycline, was administered mainly by drip infusion for a series of study in the pediatrics field, and the results were as follows: 1) DOTC (100 mg) was dissolved in a 100 ml of glucose solution and 2--3 mg/kg was administered intravenously. When the total infusion time was adjusted between one to two hours, the peak serum level of DOTC was seen at the end of infusion in each case. The serum level in a two-hour infusion time, however, the serum level was delectable for a long period of time: the serum level after 10 hours was 0.82--1.23 micrograms/ml. Above results suggest that DOTC intravenous should be given in a two-hour infusion twice a day for applicable infections in the pediatrics field. 2) Urine excretion of DOTC was about a half (50%) of the administered dosage. 3) DOTC was given mostly at about 3--5 mg/kg per day (twice a day) infusion to 25 children with five infections, viz. acute angina lacunaris, acute bronchitis, bronchopneumonia, Mycoplasma pneumonia and acute urinary tract infections. A clinical improvement seemed attributable to DOTC was clearly observed in 23 out of 25 patients (92%). 4). DOTC infusion was also effective for Mycoplasma meningoencephalitis, severe Mycoplasma pneumonia associated with pleuritis, bronchitis and bronchopneumonia with a lot of Staphylococcus aureus identified in the sputum medium, acute urinary tract infections caused by E. coli. 5) Before and ten days after DOTC infusion, laboratory tests for liver and renal functions and blood were performed. No noticeable abnormalities were found except one case with transient GOT and GPT elevations. Above summary was presented at the 26th annual meeting of Japan Society of Chemotherapy in June 1978.