The recently discovered class of cyclic hexadepsipeptide antibiotics is exemplified by azinothricin1) and A83586C2). In our search for novel substances with C5a antagonistic properties, a member of this class, L-156,602, was isolated from a newly isolated strain of streptomycete and found to be a competitive inhibitor of the binding of the anaphylatoxin C5a to its receptor on human PMNs3). Because of its broad range of biological properties, C5a has been implicated as a causative or aggravating agent in a variety of inflammatory and allergic diseases4'5) and an inhibitor of such inflammatory actions would therefore be therapeutically beneficial in the treatment of such diseases. The producing organism, MA-6348, was isolated from a plant rhizosphere soil sample obtained from a Japanese garden. Comparison of spectral data suggested the compound to be identical to PD 124,966, but no structure has been published6'7). We report here primarily on the structure determination of L-156,602 including absolute stereochemistry, based on spectroscopic and X-ray diffraction analyses. The culture was characterized by the International Streptomyces Project procedures described by Shirling and Gottlieb8*. Pigment production, carbohydrate utilization and other diagnostic tests indicated that this culture was a unique strain of Streptomyces. A complete summary of culture characteristics is available upon request from the authors.