The occurrence of the Pasteur effect in Saccharomyces cerevisiae in several conditions has been examined. In these conditions measurements of a series of metabolites potentially involved in the regulation of the effect were performed. These included, among others, adenine nucleotides, citrate, fructose 2,6-bisphosphate and phosphate. Only phosphate changed in a consistent way, increasing in anaerobiosis when the Pasteur effect occurred. It is concluded that, with the available data, only phosphate may be considered as a regulator of the Pasteur effect in this microorganism.