  The deconfinement phase transition from hadronic matter to quark matter in
the interior of compact stars is investigated. The hadronic phase is described
in the framework of relativistic mean-field (RMF) theory, when also the scalar-
isovector $\delta$-meson effective field is taken into account. To describe a
quark phase the MIT bag model is used. The changes of the mixed phase threshold
parameters caused by the presence of $\delta$-meson field are investigated.
