The effect of yeast extract/sugar ratio on the growth of Schizosaccharomyces pombe was investigated using a complex-synthetic medium. Analysis of batch cultures shows that this ratio determines the efficiency of sugar-biomass conversion. The yeast extract/sugar ratio is correlated to biomass yield by means of a Monod-type function at low and high glucose concentrations. Influence of the substrate concentration appears to be negligible in comparison to yeast extract/sugar ratio effect in this kind of medium.