This work was done as the first part of a continuing study of neonatal blood. In a recent paper (1), two parameters, "A" (relative whole-blood viscosity at unit rate of shear and 1% haematocrit) and "beta" (shear-sensitivity exponent) were proposed, as characteristics of a given blood-sample. Here, some 60 placentae yielded (after plasma-manipulation) 130 sub-samples having haematocrits ranging from 3% to 90%. Their viscosities were measured in a capillary viscometer set for a constant wall shear-stress of 1855 mPa. "A" and "beta" were calculated by the method given in (1). Multiple calculations on a number of sub-samples revealed systematic variations within any one blood; but when every A/beta ratio is plotted against the corresponding A, the results follow a smooth curve. This curve occupies a striking, almost central location when A-and-beta values from adult normal and pathological bloods (rotational viscometry) are superimposed on the diagram. An analytic form for the close correlation between haematocrit and relative placental blood-viscosity is given by the adoption of a single "group A" and "group beta" for all 130 results.