An intravenously acceptable aqueous tetracycline-containing solution in which 5 to 50 milligrams of activity per millilitae remain in solution for at least 24 hours is prepared by intermixing tetracycline or a salt thereof with sufficient non-toxic acid and water to provide a solution having a pH of 1.5 to 3.0 and preferably 2.0 to 2.4 sufficient free acid being present to prevent hydrolysis of the tetracycline salt. Two containers may be used one for the tetracycline and one for the acidified ...