  Let F be a finite extension of Qp and G be GL(2,F). When V is the tensor
product of three infinite dimensional, irreducible, admissible representations
of G, the space of G-invariant linear forms has dimension 0 or 1. When a
non-zero linear form exists, one wants to find an element of V which is not in
its kernel : this is a test vector. Gross and Prasad found explicit test
vectors when the three representations are unramified principal series, and
when the three representations are unramified twists of the Steinberg
representation. In this paper, we find an explicit test vector when two of the
representations are unramified principal series and the third one has
ramification at least 1.
