  A novel method for detecting Luttinger-liquid behavior is proposed. The idea
is to measure the tunneling conductance between a quantum wire and a parallel
two-dimensional electron system as a function of both the potential difference
between them, $V$, and an in-plane magnetic field, $B$. We show that the
two-parameter dependence on $B$ and $V$ allows for a determination of the
characteristic dependence on wave vector $q$ and frequency $\omega$ of the {\it
spectral function}, $A_{\rm LL}(q,\omega)$, of the quantum wire. In particular,
the separation of spin and charge in the Luttinger liquid should manifest
itself as singularities in the $I$-$V$-characteristic. The experimental
feasibility of the proposal is discussed.
