The energetics of growth of the fission yeast Schizosaccharomyces pombe was studied in continuous high-cell concentration cultures using a cell-recycle fermentor. Under non-O2-limited conditions, steady-states were obtained at various specific growth rates (partial cell-recycle) with purely oxidative (glucose limitation) or respiro-fermentative (glucose excess) metabolic behaviour. The stoichiometry of biomass synthesis was established from the elemental composition of the cells and measurements of all the specific metabolic rates, i.e. consumption of glucose and O2 and production of CO2, ethanol and other products. The theoretical yield factor for biomass on glucose was YG,X = 0.85 C-mol.C-mol-1 and maintenance requirements were negligible. Assuming a constant coupling between energy generation and biomass formation for both respirative and respiro-fermentative breakdown of glucose, the biomass yield from ATP (YATP) and the efficiency of oxidative phosphorylation (P/O ratio) could be determined as 9.8 g biomass.mol ATP and 1.28 mol ATP.atom of O2, respectively.