  We study the implication of decoupling zero-norm states in the high-energy
limit, for the 26 dimensional bosonic open string theory. Infinitely many
linear relations among 4-point functions are derived algebraically, and their
unique solution is found. Equivalent results are also obtained by taking the
high-energy limit of Virasoro constraints, and as an independent check, we
compute all 4-point functions of 3 tachyons and an arbitrary massive state by
saddle-point approximation.
