  We find the defining equations of Rees rings of linearly presented height
three Gorenstein ideals. To prove our main theorem we use local cohomology
techniques to bound the maximum generator degree of the torsion submodule of
symmetric powers in order to conclude that the defining equations of the Rees
algebra and the special fiber ring have the same image in the symmetric
algebra. We show that this image is the unmixed part of the ideal generated by
the maximal minors of a matrix of linear forms which is annihilated by a vector
of indeterminates, and otherwise has maximal possible grade. An important step
of the proof is the calculation of the degree of the variety parametrized by
the forms generating the grade three Gorenstein ideal.
