Abstract: A process for preparing whole blood reference controls having long term stability up to six months for devices using electronic means for whole blood determinations including platelet count and mean cell volume and red blood distribution width. The preconditioning diluent for the red blood cells consists essentially of an aqueous solution of lactose, sodium azide, and a non-ionic surfactant and is pH buffered and osmolality adjusted. The media of the whole blood control includes lactose, fungicides and antibiotics, and supplementary agents including purine nucleosides. It also includes additional components which alter red blood cell membranes including bile salts and cholic acid derivatives, phenothiazine compounds and the salts thereof having antihistamine properties, and 4-aminobenzoic acid ester derivatives and their salts having local anesthetic properties.