The isolation, structure, and biol. properties of SNA-4606-1 (I), a new elaiophylin with enzyme inhibition activity against testosterone 5α-reductase, are reported.I was extracted from the mycelium of Streptomyces SNA-4604.The structure of chromatog. purified I was elucidated by COSY and other spectroscopic analyses.I inhibited rat prostate testosterone 5α-reductase.Efomycin G and elaiophylin, isolated from the same source, showed similar inhibitory activity.