A method is described for isolation of grail quantities of the components of the streptothricin complex S15-1 utilizing CM Sephadex column chromatography eluted with 10% acetic acid as an eluant followed by gradient elution with 10% acetic acid containing 0.02N-0.03 N HCl. Streptothricins F and E, as well as an unidentified component C¹, have been isolated and their comparative biological activities determined. Streptothricins F and E were comparable in taeniacidal activity in mice infected with Hymenolepis nana as feeding either one at 0.05% in the diet removed 92-100% of the adult tapeworms. The unidentified component C¹ was inactive at the levels tested. In contrast, component C¹ was the most active in antimicrobial activity against Bacillus subtilis and in inhibiting the urcase activity of Proteus mirahilis. In the former test, the ratios of activity were; 1 : 7: 30 for F: E : C¹ and in the latter; 1 : 2: 4 for F: E: C¹.