Submerged cultures of four Streptomyces species accumulated triacylglycerol (TAG), ranging from 50 to 150 mg (l medium)-1, during the post-exponential phase of growth. S. lividans also produced glycogen (80 mg l-1). Identity of TAG species was confirmed after TLC, by mass spectroscopy and by quantitative IR spectroscopy and reaction of the hydroxamate derivatives with ferric chloride. This is the first substantive report showing the storage of TAG in bacteria. Distribution of diacylglycerol acyltransferase (TAG synthase) activity from S. coelicolor and S. lividans during incubation on different media paralleled the formation of TAG. Accumulation of TAG may be necessary to maintain cell integrity after glucose becomes exhausted from the medium, and also to provide the C2 units needed for subsequent biosynthesis of acetate-derived antibiotics in appropriate species. Actinorhodin was formed by S. coelicolor when grown on YEME medium only after exhaustion of glucose; the carbon source may therefore originate from TAG. All the organisms examined in this study formed isoprenoid-derived hydrocarbons (up to 3 mg l-1) which were identified as squalene plus hydrogenated derivatives.