ultradian rhythms have been extensively studied in the functioning of the physiological and psychological systems. the purpose of this research was to explore the nasal cycle which has been coupled to both the autonomic and central nervous systems. the nasal cycle consists of alternating lateral vasoconstriction and vasodilation of nasal mucosa. specifically, predominant airflow through one nostril has been linked to the activity of the contralateral hemisphere. from a review of the literature of hemispheric specialization, the right hemisphere has been shown to be associated with spatial abilities, whereas the left hemisphere has been shown to be the predominant site for veribal and arithmetic functioning. hemispheric specialization in terms of cognitive style has been demonstrated to be associated with the nasal cycle. additionally, both sympathetic and parasympathetic branches of the autonomic nervous system fluctuate as a function of nasal airflow rhythms. this study investigated the effects of forced unilateral nostril breathing on specific cognitive styles and sympathetic vs. parasympathetic nervous systems. subjects, who were recruited from introductory psychology classes and tested in groups, were asked to breathe through the left or the right nostril, or to breathe freely during a relaxation procedure. cognitive tests assessing arithmetic and spatial performance and tests assessing autonomic tonus were administered both before and after the experimental procedures. it was predicted that predominant airflow through one nostril will be associated with the activity of the contralateral hemisphere as assessed by the cognitive tests. additionally, left nostril dominance was predicted to be associated with parasympathetic activity, whereas right nostril dominance was predicted to be associated with sympathetic activity. this study did not reveal results that support the hypotheses. the nasal passage was open at the end of the study in the predicted direction in only about half the subjects. since the experimental manipulation did not open the nasal passage as expected, no conclusive statements about the interactions between the nasal cycle and the central and autonomic nervous systems can be drawn from this study.