Abstract: A chemostat apparatus and a whole glass fermentor were used in the continuous culture of Anabaena vasriabilis. When diurnal light-dark cycles (12:12 h) were incorporated in the stable conditions of the cultivation, a semi-steady state of the culture was achieved in 5-6 days. The periodic change rates of biomass were different from those of other growth parameters. The metabolic features of the culture under the L:D cycles could be i licated by the comparative data on the synthesis and accumulation of cell components (e.g., glycogen and protein) over the time course. The growth of the culture showed an innate physiological regularity. Changes of the growth parameters can be described by the equation X=Xoeμ-Dt. This semi-steady state of continuous culture was different from chemostatic and turbidostatic cultures. The technique is suitable for the research of algal ecophysiology and algal biotechnology.