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 spectral function, A(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 characteristics. The experimental feasibility of the proposal is discussed.