An associative algebra A(R) with exchange properties generalizing the
canonical (anti)commutation relations is considered. We introduce a fa
mily of involutions in A(R) and construct the relative Fock representa
tions, examining the positivity of the metric. As an application of th
e general results, we rigorously prove unitarity of the scattering ope
rator of integrable models in 1+1 space-time dimensions. In this conte
xt the possibility of adopting various involutions in the Zamolodchiko
v-Faddeev algebra is also explored. (C) 1997 American Institute of Phy
sics.