Erythromycin A is a 14-membered macrocyclic lactone with broad spectrum antibiotic activity, isolated from Saccharopolyspora erythraea (formerly Streptomyces erythreus) in 1952. Erythromycin is one of only a handful of microbial metabolites to have profoundly shaped the treatment of bacterial disease in the last 50 years. Erythromycin has given rise to new generations of semi-synthetic derivatives with improved stability and potency. Our product has been HPLC-purified to remove contaminants and degradation products.