The cytosol fraction purified from cellular organelles was obtained from S. cerevisiae yeast cells. This cytosolic fraction contained a polyphosphatase activity comprising nearly 65% of such in the protoplast homogenate. The pH optimum of this activity was 6.5-7.5. Bivalent metal cations stimulated the polyphosphatase activity 9-14-fold in the following order: Zn2+ > Co2+ > Mg2+, Mn2+. Fe2+, Cu2+ and Ca2+ ions inhibited this activity at all concentrations used. The cytosolic polyphosphatase was effectively inhibited by molybdate and heparin. Heparin was effective only in the presence of Mg2+, Mn2+ and Co2+ but had no effect in the presence of Zn2+. Heparin inhibited polyphosphatase competitively. The polyphosphatase activity was the same with poly (P)9-poly (P)208. On poly (P)9, poly (P)15 and poly (P)208 the Km(app) values were equal to 19, 11, 1.2 microM, respectively. The molecular mass of cytosolic polyphosphatase determined by gel filtration on Sephacryl S-300 was 50 kDa.