Myxobacteria of the genus Sorangium have proved in the last few years to be extremely versatile producers of biologically active secondary metabolites. This diversity is true both for the basic structures, which are generally new, and for the biological effects and their underlying mechanisms. Sorangia very frequently produce antifungal compounds, which may be explained by the fact that these cellulose-degrading organisms have to compete with fungi for the same ecological niche. Also, the Sorangium cellulosum strain Soce90 was identified during screening by its antifungal activity, which guided the isolation of two new, structurally unrelated classes of compounds, the epothilones and the spirangiens. When isolated in the pure form, epothilones A and B (1a and 1b, respectively) showed broad activity against eukaryotic cells; the efficiency of the methyl derivative B was mostly a factor of 2 greater than that of the derivative A. The antifungal activity of 1 against oomycetes (Plasmopara viticola, Phytophthora infestans), in vitro and in the greenhouse, is noteworthy, as is its cytotoxicity against mouse fibroblasts (cell line L929, 1b: IC50 2 ngmL-1), which results in disintegration of the cell nucleus and apoptosis (programmed cell death) within three days. The epothilones also showed noticeable activity and selectivity against breast and colon tumor cell lines in the in vitro antitumor screening program of the National Cancer Institute (NCI). In addition, epothilones were discovered independently by Bollag et al. by a tubulin polymerization assay. This assay, and subsequent detailed studies of their cytotoxicity and inhibition of mitosis show that the epothilones have an almost identical activity and mode of action to that of taxol and, according to the results of displacement experiments, apparently compete for the same binding site on microtubules. These discoveries resulted in much interest in the production of epothilones, their three-dimensional structure, and potential homology to taxol, which will be reported herein.