Dried, crude tetracycline dibenzylethylenediamine (2 kg.) activity 680 .gamma./mg. (Brit. 936,314) was suspended in 20 1. H2O, dil. HCl added to pH 2.9, 300 g. Na or K hexametaphosphate (I) in 31.H2O added with stirring, pH adjusted to 2.2 and the supernatant decanted. The soln. was treated with 250 g. in 2.5 l. H2O, and pH adjusted to 1.7 to give the Na or K hexametaphosphate tetracycline complex (83%), with microbiological activity 808 .gamma./mg.