Taurine concentrations are 400-fold greater in platelets than in plasma1, 5. The role of taurine in platelets has not been elucidated. For cardiologists, platelet taurine content is likely to have diagnostic value, since a decrease in taurine concentration in these cells indirectly reflects changes in taurine level in body tissues in general and in heart in particular11. Paasonen et al. 12 have reported that the taurine level in patients with hypertension does not differ from control values but increases in patients with myocardial infarction. In platelets, taurine transport decreases both in hypertension and in cardiovascular failure9. Marked losses of taurine from animals or humans affects the functional state of not only such organs as heart13 and retina8 but also of platelets. Taurine is known to model Ca2+ responses to PAF3. Taurine can inhibit PAF-induced aggregation of guinea pig platelets and aggregation of human platelets induced by ADP, serotonin and epinephrine2. Hayes et al. 9 reported the interrelation of taurine status and platelet aggregation in cat. They discovered that marked loss of taurine from platelets make them more sensitive to aggregation. These authors assume that this effect can be mediated via changes in GSH and altered thromboxane liberation. We suppose that this effect of taurine is not its only platelet action. Taurine may possess a homeostatic action that is revealed in certain pathological conditions. For this reason we have studied taurine effects in cells obtained from donors with different rhythm disturbances.