  We study matrix three term relations for orthogonal polynomials in two
variables constructed from orthogonal polynomials in one variable. Using the
three term recurrence relation for the involved univariate orthogonal
polynomials, the explicit expression for the matrix coefficients in these three
term relations are deduced. These matrices are diagonal or tridiagonal with
entries computable from the one variable coefficients in the respective three
term recurrence relation. Moreover, some interesting particular cases are
considered.
