Bacterial variants that lack a cell wall are known as L-forms and can be induced under conditions that interfere with cell wall synthesis. Claessen and colleagues now report that when filamentous actinomycetes are exposed to osmotic stress they extrude previously undetected cell wall-deficient cells, which they termed S-cells. Formation of S-cells seems to be common in filamentous bacteria, as they occur in Streptomyces and Kitasatospora species in response to hyperosmotic stress. S-cells extrude from the hyphal tips into the environment, contain DNA and are larger than 2 µm in size (distinguishing them from spores). This cell wall-deficient state is transient as S-cells can switch to the canonical mycelial growth mode, although those switched colonies exhibit developmental defects. Finally, following prolonged exposure to osmotic stress, some cells acquire mutations and convert into L-forms that can proliferate indefinitely in the cell wall-deficient state. In sum, S-cells may represent a newly identified developmental stage that enables actinomycetes to thrive under hyperosmotic stress conditions.