A new cytostatic compound, rhizopodin, was isolated from the culture broth of the myxobacterium, Myxococcus stipitatus. The compound inhibited growth of various animal cell cultures without killing the cells. The ID50, measured by an MTT assay, was 12 approximately 30 ng/ml, depending on the cell line. Especially cells growing fibroblast-like showed typical morphological changes. They became larger and within hour formed long branching and reticular runners. These morphological changes were irreversible. Rhizopodin suppresses bleb formation in K-562 cells, and therefore could act by interacting with protein phosphorylation.