A chlorophyllous cell Line of liverwort, Marchantia paleacea var. diptera, exhibited good photoautotrophic growth in a light-irradiated culture with an air supply containing 1% CO2 as the sole carbon source. In cultures with flat, oblong glass flasks under various conditions of light intensity, a plot of light intensity against the specific growth rates of these cells revealed that light exerted both stimulatory and Inhibitory effects on growth. More specifically, the specific growth rate increased with an increase in light intensity over the range of 5.4 to 60 W/m(2), while a significant decrease in the rate occurred when light intensity was greater than 60 W/m(2). Photoautotrophic suspension cultures of M. paleacea cells were conducted using an externally illuminated reactor. The distribution of light intensity in the reactor was analyzed on the basis of the relation between light transmittance and cell concentration in medium. The behavior of cell growth in the reactor could be described by taking into consideration the dependence of cell growth on light and the attenuation of light intensity in the cell-suspended medium.