The form of the sporulation septum in Streptomyces appears to have taxonomic value but its demonstration has hitherto required electron microscopic study of ultrathin sections. This lengthy procedure has limited the use of sporulation to provide characters for identification and taxonomic purposes. It has now been shown that there is good correlation between the width of the sporulation septum and the type of sporulation, and that the septum can be measured in negatively stained preparations. The latter technique is relatively simple and rapid, and we now advocate its use to give an additional character for Streptomyces taxonomy.