Aim To study the changes of volume.function and characteristics of L-arginine(L-Arg)transport of platelet(Pt)in patients with essential hypertension (EH).Methods Nitric oxide(NO)production by platelets was assayed by measuring the accumulation of nitrite in the incubation medium using Greiss reaction accord-ing Green' method.Transport of 3H-L-Arg was determined essentially as described by William.In-flux of 3H-L-Arg was determined by measuring cell-associated radioactivity after an approprite period of in-cubation with 3H-L-Arg.Results in EH patients,the quantity and volume of Pt has no obvious difference with the normal.The maximum platelet aggregation ratio(PAR)was much higher than that in normal(P<0.05)and PAR was correlated with NO production.The production of NO and the ability of L-Arg transport in EH was re-spectively lower than that in normol(P<0.01).Maxi-mum transport velocity(Vmax)in EH was only 79%of normal(P<0.01).While the Michael constant (Km)showed no significant difference between the two groups.Conclusion Above results indicate that there exists a founctional and L-Arg transport disturbance in EH.It appears that the improvement of NO production and L-Arg transport in treatment of hypertension may be potentially important.