This study examines the influence of so-called biorhythms on circulatory parameters (heart rate, systolic and diastolic blood pressure) at rest and during ergometric exercise. It was not possible to predict individual responses based on a postulated biorhythmic periodicity of 23 and 28 days and on the birthdate in any uniform manner. The positive effect of the positive phase and negative effect of the negative phase postulated by the biorhythmy was not found. No connexion was found between the subjective condition of the probands and any rhythm at all. At the significance level (p = 0.05) the differences of the variables (systolic and diastolic blood pressure, as well as heart rate) were found only in short phases of the examination and were not observed through out the whole experiment. The differences in the response of the parameters in male and female subjects points to the existence of sex-specific rhythms. The results of multivariance analysis show the existence of the "rhythm" factor. Hence, it is probable that every person has his own individual rhythm, or system of rhythms. It is not possible to prove and reproduce these individual rhythm by means of tables, diagrams etc.