The invention relates to Cosynthetic Factor-1 (CF-1) and a process for the production of a tetracycline antibiotic by growing under aerobic conditions in an aqueous nutrient medium in the presence of CF-1 a culture of a species of Streptomyces which produces said antibiotic. CF-1 is produced by cultivating a CF-1 producing strain of Streptomyces in an aqueous nutrient medium containing assimiliable sources of carbohydrate, nitrogen and inorganic salts under submerged aerobic conditions until substantial CF-1 activity is imparted to said medium, filtering the fermentation mash at pH 6 to 7 and recovering CF-1 from the aqueous filtrate. It is preferred to use Streptomyces aureofaciens W5 (ATCC 13190), described, but others specified are S. albus, S. rimosus NRRL 2234, S. platensis NRRL 2364, S. hygroscopicus, S. viridifaciens ATCC 11989, S. griseus (streptomycin) and S. albo-niger (puromycin). The broth filtrate is adjusted to pH 8-9, saturated with ammonium sulphate, a carrier particularly a long chain alkyltrimethylammonium chloride added and the mixture is extracted with an alkanol such as butanol. The extract is adjusted to pH 1.5 to 2.0 with hydrochloric acid and back extracted with water. The aqueous phase is concentrated, chromatographed on diatomaceous earth and developed with buffered n-butanol. CF-1 rich cuts are extracted with water, concentrated, chromatographed on "Florisil" (Registered Trade Mark), eluted with methanol, adjusted to pH 1.0 with hydrochloric acid and the CF-1 recovered. Cosynthetic factor-1 is soluble in phenol and in water at pH > 6, insoluble in butanol, acetone, ether and water at pH 1-2; it contains the elements C = 50.33, H = 5.00, N = 12.18 and O = 32.49% by weight, empirical formula C14-15H17N3O7; melting point 280-285 DEG C.; the acid form has the infrared absorption spectrum shown in Fig. 1 and the ultraviolet absorption spectrum shown in Fig. 3. Specifications 775,115 and 863,419 are referred to.