In this fermenter, the culture is circulated around a closed loop to effect aeration, mixing, and homogeneous cultivation of the cells, instead of by agitation and stirring in a tank, as in most conventional fermenters. The culture vessel consists of a vertical glass column with a pump continuously recycling the culture from the bottom to the top of the column. The culture is introduced tangentially through a cyclone head with considerable kinetic velocity so that it falls as a thin film spinning down the wall back to the pump for recirculation. Air or a suitable gas mixture introduced at the bottom of the column rises countercurrent to the flow of the culture. The vessel operates without need for antifoam, prevents wall growth, and gives representative samples. It is simple to use, reliable in operation, and suitable for cultivating aerobic or anaerobic nonpathogenic microorganisms. A laboratory-scale apparatus having a culture capacity of 500 to 1,000 ml and a tenfold scaled-up version of this suitable for pilot-plant studies are described, and the operating procedures outlined. The vessels can be used for batch or continuous growth of asynchronous or synchronous cultures. Several modifications and applications of the equipment are given.