It is shown that the technique recently suggested by Brown for summing the tree graphs at threshold can be extended to calculate the loop effects. An explicit result is derived for the sum of one-loop graphs for the amplitude of threshold production of n on-mass-shell particles by one virtual particle in the unbroken gamma phi4 theory. It is also found that the tree-level amplitude of production of n particles by two in-coming on-mass-shell particles vanishes at the threshold for n > 4.
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