In patients with essential hypertension, increased level of platelet activity expressed as the concentrations of p-thromboglobulin (β-TG) and platelet factor 4 (PF4) were observed. Elevation of the levels of both β-TG and PF4 correlated with the increase in platelet aggregability in platelet-rich plasma (PRP) and the decrease in red blood cell deformability, which were considered as being the possible factors for the platelet intravascular activation. After 2 weeks of monotherapy with nifedipine (40 mg daily), a decrease in platelet aggregability in PRP was observed in 35 of the 75 patients and an increase in red cell deformability in 37 of the 75 patients. Using cluster analysis, all cases were divided into several groups based on nifedipine effects on red cell deformability and platelet aggregability in PRP. It was revealed that the statistically significant decrease in the levels of platelet markers took place only in patients in whom nifedipine simultaneously decreased platelet aggregability and increased red cell deformability. Analysis of variance showed a high power of influence for combined changes in these parameters for reducing intravascular platelet activation by nifedipine. It is suggested that nifedipine reduces platelet activity by direct action on platelets and indirectly due to its capacity to increase red cell deformability, resulting in elimination of platelet stimulation by red blood cells.