Abstract: A blood analyzer is provided with means to automatically pierce the sealed closure of a vacuum container or to aspirate through an aspirator tip blood samples to be analyzed. The samples are drawn serially through a repositionable valve structure, preferably of rotary form, and having three members in layers with aligned ports in one position to receive the blood that is drawn through the valve by a syringe type aspirator. Another position of the valve connects diluent supplies providing measured amounts of diluent to wash out the bores of the middle member of the valve containing amounts of blood measured by the size of the bores. In the case of the red blood cell measurement, where the bore is extremely small, a larger by-pass port is provided in parallel with the sample containing bore to allow more rapid flow simultaneously through both.Blood analysis is performed by separate conventional cell counter arrangements for each of the red and white counts.