1. In liver extracts fructose-1-phosphate is split into dihydroxy-acetone-phosphate and glyceric aldehyde by an enzyme („1-phospho-fructaldolase”) which is different from cristalline muscle aldolase („1,6-diphosphofructaldolase”). The reaction is independent of Mg++-ions. (Most of the reactions described in this paper have been followed by optical tests using the reduction of D.P.N. or the oxidation of (D.P.N.) H2).