Abstract
An experiment is discussed, where a simple binary choice task is used with several frequencies of signals to be answered and so with different loads. Systematic changes were found in heart frequency, sinus arrhythmia, systolic and diastolic blood pressure, rate of respiration, a.s.o. Arguments are put forward that these changes are due to a simultaneous rise in symphatical and in vagal tone. Some situations where mental load might be important are discussed. To estimate or to measure the mental load in such situations some methods are suggested.