The Ca2(+)-ATPase activity and calmodulin (CaM) of erythrocytes and the effect of nifedipine on them were studied in subjects with essential hypertension (EHT). The results showed that both the basal and maximal Ca2(+)-ATPase activities of erythrocytes were lower in subjects with EHT than those in normal controls, and Ca2+a-ATPase activities were negatively correlated with blood pressure; the content of CaM was also reduced, and it was positively correlated with maximal Ca2(+)-ATPase activity. The basal Ca2(+)-ATPase activity was improved with nifedipine, but the maximal Ca2(+)-ATPase activity and CaM content were both unchanged significantly. Thus, the Ca2(+)-ATPase and CaM of erythrocytes might play an important role in EHT, and nifedipine has a mild effect on cellular calcium transporting.