TETRACYCLINE is a recently developed antibiotic which has a structure2 and antimicrobial spectrum * similar to those of chlortetracycline and oxytetracycline. To evaluate its clinical usefulness and pharmacologic properties, we have studied the effect of the oral and intravenous administration of tetracycline, as the hydrochloride, in 184 patients with acute infections. All adults were given a dose of 2 gm. a day, and children were given 50 mg. per kilogram of body weight a day, in four divided doses at six-hour intervals. The adult patients treated orally were given an initial dose of 1 gm., and the children were given a dose of 25 mg. per kilogram of body weight, for the purpose of obtaining a higher initial serum level. The clinical course in 153 of the 184 patients was evaluated on the basis of duration of fever, leucocytosis, subjective complaints, and objective physical findings (Table 1). The response of