A new isolation method for endothelial cells from blood together with platelets and with the
subsequent removal of the latter is described. The method allows a quantitative estimation of
the endothelial cell count. Their number increased significantly in rats after an intravenous
injection of acidified citrate solution. An intravenously administered hydroxyethyl-rutoside
preparation, Venoruton, blocked the effect of citrate. The mechanism of action of the drug
was subjected to a more detailed investigation.