SUMMARY: The design and construction of a continuous culture apparatus with a 2 1. culture vessel are described. Aeration is achieved by means of a mechanical stirrer and injected air, automatic temperature and pH control are features of the apparatus, and foaming is controlled by adding antifoam through a manually operated valve. A high degree of agitation ensures that good mixing takes place. Accurate and easily variable control of the medium flow rate is obtained by means of the Mariotte bottle principle. The apparatus can be operated continuously with freedom from contamination for periods in excess of 1000 hr.