Blood viscosity of 125 healthy men in the age group of 45–55 yr was studied by means of the rhombospheroid viscometer on EDTA blood at 37°C. These data are compared with the 1966 results of Dintenfass, Julian and Miller (Am. Heart J. 71 (1966), 687) and results of Dintenfass (Circ. Res. 11 (1962), 233) obtained by means of the cone-in-cone viscometer on freshly shed not anticoagulated blood; and with the data of Copley (Biorheology 10 (1973), 87) and Copley and King (Biorheology 10 (1973), 17) (and also of Merrill (J. appl. Physiol. 18 (1963), 255). All these data superimpose at shear rates above 0.4 sec−1. At medium and low shear rates the rhombospheroid data present a better fit with the Copley and King (Biorheology 10 (1973), 17) data than the early results obtained by means of the cone-in-cone viscometer. At high shear rates results obtained by GDM, cone-in-cone (Dintenfass, Julian and Miller, Am. Heart J. 71 (1966), 687), rhombospheroid and Weissenberg viscometers are nearly identical.
