To provide information on algal growth regulators, the first phase of the investigation was a continuous flow culture study in which algae were grown under various conditions. The second phase was a batch culture study which provided means for comparing the two types of cultures (i.e., batch and continuous) and verification of some conclusions of the continuous culture study. Even in sewage effluents containing significant concentrations of both organic and inorganic carbon, algal growth was limited by availability of carbon dioxide. Where nitrogen is deficient in solution, algal succession may occur with shifts to certain blue-green forms containing atmospheric nitrogen fixing capabilities. A previously developed kinetic theory which describes algal growth as being proportional to the cellular concentration of the growth regulating nutrient was confirmed.