It was hypothesised that choice reaction-time (CRT) testing would cause salivary [K + ]/[Na + ] to increase. Relative contributions of [K + ] and [Na + ] to ratio changes were investigated in 23 hypertensives and ten hospital staff. Changes in post-rest and post-test ionic concentrations and [K + ]/[Na + ], replicated earlier studies. Phasic [K + ]/[Na + ] changes were mainly due to [K + ] changes. Significant increases in [K + ] and decreases in [Na + ] from a relaxed session, the day before CRT testing, to the testing session per se indicated test anticipation effects. In both groups, changes from pre-test “rest” to “on test” were significant only for [K + ]. [K + ] discriminated well between conditions in hypertensives. This was interpreted in terms of adaptive changes in sympathetic activation. Results show the robustness of salivary ion indices (especially of [K + ]) as indicators of within-subject response to mental task demands.