The hypocrellin B (HB)-sensitized photodamage on Na(+)-K+ ATPase and sodium permeability of human erythrocytes by means of NMR and biochemical techniques was studied in this paper. The decrease of the enzyme activity and increase of intracellular sodium concentration were usually observed simultaneously. The evidences suggested that the integrality of membrane phospholipid played an important role in maintaining the physiological sodium content of erythrocytes. The loss of the enzyme activity was a sensitive index compared with the increase of intracellular Na+ concentration during the photosensitization. From the comparison tests among HB, HA, protoporphyrin and bilirubin, we found that HB had more ability to increasing intracellular Na+ concentration than the other photosensitization even though the photodamage on the enzyme activity caused by HB, HA, and protoporphyrin were nearly the same. Besides the photoinactivation of Na(+)-K+ ATPase induced by HB and light, the enzyme was also inactivated in the medium containing HB in absence of light. The active oxygen radicals generated though HB mediated redox-cycling might be involved in the dark inactivation of the enzyme.