Results from the red cell shape analyses of 5-drop samples of immediately-fixed venous blood from 620 male and 1558 female members of myalgic encephalomyelitis (ME) organisations in New Zealand, Australia, South Africa and England are reported. Both the age spectra and the male to female ratios of the participants are very similar. Increased percentages of flat cells are. the most frequent change in both sexes in all four countries although the increases are much higher in the English results than in those from the southern hemisphere countries. Because the poor filtrability of ME blood which had been reported earlier could have been a consequence of red cell shape transformation, it is considered that the results reported here would support a propusal that ME is a hemorrheological disorder in which symptoms are manifestations of the consequences of impaired capillary blood flow. If this proposal can be confirmed by further investigations of blood filtrabiility and blood viscosity, then attention would be directed to the therapeutic potential of hemorrheological agents.