Consider I-n(K), the set of solutions to the equation X-2 = 0 in n x n stri
ctly upper-triangular matrices over field K. In this paper we construct the
bijection from the set of adjoint orbits in I-n(K) onto the set of involut
ions in symmetric group S-n. For a finite field K we compute the number of
points in the orbits. (C) 2000 Academic Press.