  The gyrokinetic stability of electron-positron plasmas contaminated by ion
(proton) admixture is studied in slab geometry. The appropriate dispersion
relation is derived and solved. The ion-temperature-gradient driven
instability, the electron-temperature-gradient driven instability, the
universal mode, and the shear Alfven wave are considered. The contaminated
plasma remains stable if the contamination degree is below some threshold, and
it is found that the shear Alfven wave can be present in a contaminated plasma
in cases where it is absent without ion contamination.
