The authors analyze in detail all substantial factors which influence the red cell sedimentation. They express this one a function of time, hematocrit, hemoglobin concentration, concentration of some plasma proteins, citrate density and viscosity. These values serve to describe the plasma and red cell density, plasma viscosity, red cell aggregation and to express the influence of the hematocrit on the red cell sedimentation. The authors try to quantify all influences in order to differentiate important factors from less important ones. Finally they demonstrate on several case-histories the necessity of a rational analytical attitude to values of the red cell sedimentation rate.