Phenomenological constraints on the flavour asymmetry of the nucleon sea

We study the possible flavour asymmetry, $\bar{u} \neq \bar{d}$, of the light quark sea distributions of the proton. We discuss the information that is at present available from data on deep-inelastic lepton-nucleon scattering and from Drell-Yan production on various nuclear targets. We show that the ratio of dilepton yields on hydrogen and deuterium targets is very sensitive to $\bar{u}-\bar{d}$.