A system has been developed for the culture of algae on a 3–5 l scale under controlled axenic conditions. Light/dark regimes can be altered for the induction of synchrony and an automatic culture dilution system with new media has been developed. The results are shown for Platymonas striata. It was possible to induce synchrony by a regime of 14 h light and 10 h darkness per 24 h. This synchrony could be maintained for many cycles by the removal of half the culture daily and its replacement with fresh medium 4 h after the onset of the light period. Cell separation commenced at the onset of the light period and was completed after 4 h. No cell separation occurred during the remainder of the 24 h cycle. A system for automatic sampling of the axenic culture at known time intervals is described.