Objective: In a previous study, low-frequency (0.5 Hz) cranial electrostimulation (CES) neither improved the rest-activity rhythm nor reduced the level of salivary cortisol in patients with probable Alzheimer's disease (AD). To investigate whether the frequency of CES was responsible for these negative findings, we set out to examine the effects of high-frequency CES on the rest-activity rhythm and salivary cortisol of patients with probable AD. We hypothesized that a decreased level of cortisol would parallel a positive effect of high-frequency CES on nocturnal restlessness in AD patients. Methods: Twenty AD patients were randomly assigned to an experimental group (n = 10) and a control group (n = 10). The experimental group was treated with high-frequency CES, the control group received sham stimulation, for 30 min a day, during 6 weeks. The rest-activity rhythm was assessed by actigraphy. Level of cortisol was measured by means of salivette tubes. Results: The rest-activity rhythm and the level of salivary cortisol did not react positively to high-frequency CES. In contrast, both groups showed an increase in the level of cortisol after the 6-week treatment period. Conclusions: High-frequency CES appeared to be ineffective in AD patients.