SUMMARYMarine blue‐green algae, Lyngbya Lagerheimii, Microcoleus chthonoplastes, Plectonema terebrans, Agmenellum quadruplicatum, and freshwater blue‐green algae, Anacystis nidulans, Anabaena variabilis, Nostoc muscorura,and Oscillatoria sp. treated with lysozyme (muramidase) formed spheroplasts but not protoplasts. The time needed for spheroplast induction varied with the species. Approximate internal osmotic pressures of the blue‐green algae were determined. Marine algae generally had a higher osmotic pressure than freshwater