Chlortetracycline was the first reported member of the tetracycline class, isolated from Streptomyces aureofaciens in 1948. Chlortetracyclines heralded the early wave of antibiotic discoveries from microbes and after 50 years are still widely used as pharmaceuticals. Chlortetracycline is a pigment and, like most pigments, is extremely sensitive to environmental and storage conditions. Commercial chlortetracycline may contain significant levels of degradation products.