Glycine and formaldehyde are converted into serine in the presence of a dialyzed, lyophilized enzyme preparation from corn seedlings, with tetrahydropteroylglutamic acid and pyridoxal phosphate as coenzymes. The equilibrium constant of the reaction was calculated for the system at 37.5 °C as K = 3.1 × 103. The pH activity curve showed a maximum between 6.6 and 7.0. The effects of the concentrations of the coenzymes were studied. The glycine–serine interconverting enzyme is present throughout the seedling and occurs exclusively in the soluble fraction of the cells.