New decalin-carbonitriles of the formula I ##STR1## wherein R.sup.1 is an alkyl group with 1-10 C atoms, it being possible for up to two CH.sub.2 groups to be replaced by O atoms, Z is --CH.sub.2 CH.sub.2 --, --CO--O--, --O--CO--, --O--CH.sub.2 --, --CH.sub.2 O-- or a single bond, A is 1,4-phenylene, 1,4-cyclohexylene, 1,3-dioxane-2,5-diyl, 1,4-bicyclo(2,2,2)octylene, pyrimidine-2,5-diyl or a single bond, and R.sup.2 is an alkyl group with 1 to 10 C atoms, it being possible for up to two CH.sub.2 groups to be replaced by O atoms, or is F, Cl, Br, CN, --O--COR.sup.3 or --COOR.sup.3, or, if at least one of the groups Z and A is not a single bond, can also be H and R.sup.3 is alkyl of 1 to 6 C atoms, and the acid addition salts of basic compounds of this type, are suitable for use as components of liquid crystal dielectrics.