  We study theoretically the conductance of heterostructures with ferromagnetic
conductors (F) and a two dimensional electron gas with Rashba spin-orbit
interaction (R) using the Landauer-B\"{u}ttiker formalism. Assuming a
one-dimensional model, we first find the $S$-matrix for the FR interface. This
result is then applied to different devices such as a FRF structure, first
suggested by Datta and Das[Appl. Phys. Lett. 56, 665 (1990)]. We find analytic
results for the conductance for the case of collinear magnetization.
