Spherical protoplasts (30–40 μm in diameter), isolated from cultured tobacco cells, elongated rapidly during a culture period of 3 to 8 days and finally assumed a long cylindrical form (300–400 μm in length). The optimum concentration of a-naphthaleneacetic acid and benzyladenine for the elongation was 0.1 mg/liter and 1 mg/liter respectively.