In order to clarify the characterization of phenotypes of paroxysmal nocturnal haemoglobinuria (PNH) erythrocytes (E), we analysed the expression of decay accelerating factor (DAF) and CD59/membrane attack complex inhibition factor (MACIF) on the membrane surface of PNH-E by means of the flow cytometric method using anti-DAF and/or CD59/MACIF monoclonal antibodies in nine PNH-patients. In two-colour analysis, this expression of PNH-E was classified into three fractions; negative, intermediate and positive according to intensity. The negative fraction was classified into two groups; one group an exclusively negative population, and the other a negative population having slightly DAF-positive E. The intermediate fraction was recognized on PNH-E of cases with PNH II-E and extremely heterogenous. In the positive fraction, this expression was almost the same as on normal E except for case 8. In single-colour analysis for DAF or CD59/MACIF, three fractions were classified as well as the definition in two-colour analysis. In single-colour analysis, the expression on PNH-E was also heterogenous in each fraction and among PNH-patients. However, the intermediate fraction for CD59/MACIF was not found on PNH-E of cases without PNH II-E, although intermediate fraction for DAF was recognized on PNH-E of some cases with PNH III-E in addition to those with PNH II-E. The results suggest that expression of CD59/MACIF and DAF on the membrane surface of PNH-E phenotypes is heterogenous and varies among PNH patients.