Previous studies have shown cyclic changes in the activation levels and performance of different tasks throughout the menstrual cycle. The aim of this study was to examine if changes in the reaction time to both light and sound stimuli may be associated with basal body temperature changes and subjective assessments of General and High Activation during the different phases of a menstrual cycle characterized by high (preovulatory and midluteal phase) and low (menstrual and early follicular phase) levels of oestrogen and progesterone. The study included measurements of basal body temperature, simple reaction times to light and sound and self-assessment of General and High Activation during the menstrual, early follicular, late follicular and luteal phase. The sample consisted of 19 female subjects with regular menstrual cycles. The results obtained in this study indicate lower basal body temperature values during phases with low sex hormone levels, while the activation assessments suggest stable levels of both General and High Activation throughout the menstrual cycle. Similar patterns of change have been shown for reaction times in visual and auditory sensory modalities. Reaction times were shorter during phases characterized by high sex hormone levels, while phases with low hormone levels were associated with longer reaction times. From the modifi ed text on correlations in the data analysis section, it is evident that they were calculated from averaged data from all phases of the menstrual cycle. Therefore, they do not refl ect intraindividual but rather interindividual variations between the observed variables, and are not related to the hypotheses of this paper.