Variation of the culture conditions of Streptomyces sp. strain A1, which produces streptazolin (1), resulted in the isolation of four new co-metabolites: 5-O-(beta-D-xylopyranosyl)streptazolin (3), 9-hydroxystreptazolin (4), 13-hydroxystreptazolin (5), and streptenol E (6). Their structures were established by spectroscopic and chemical methods. The possible biosynthetic relationship between the streptazolins and the streptenols is discussed.