  In the Standard Model (SM), dilepton production in hadron--hadron collisions
proceeds through the conventional Drell--Yan mechanism $q \bar{q} \rightarrow
l^+ l^-$ with the exchange of a gauge boson. Some extensions of the SM contain
a quark--lepton contact interaction {\it via} a $q l \phi$ Yukawa coupling,
where $\phi$ is a scalar. Theories with scalar leptoquarks and $R$--parity
violating SUSY models are the most important examples of such extensions. These
Yukawa couplings induce a different dynamical configuration compared to the SM
($t$-channel vs. $s$-channel) in the $q\bar{q} \rightarrow l^+l^-$ process and
thus offer the possibility of being identifiable upon imposition of suitable
kinematic cuts. We discuss these effects in the context of the dilepton
production in the CDF experiment, and explore consequences in the forthcoming
Large Hadron Collider (LHC).
