In 1678, ages before there was any concept of blood viscosity, it was appreciated by Anthony van Leeuwenhoek (Delft, the Netherlands) that red blood cells (RBC) have to deform in order to negotiate capillary passages [1]. Using his home-made microscopes he also noticed the phenomenon of reversible red cell aggregation in relation to slow and stagnant in vivo blood flow [2]. Van Leeuwenhoek was far ahead of his contemporary scientists, and although the existence and importance of blood circulation was recognized 175 years later (i.e., around 1850 by Harvey and Virchof), studies of the flow behavior of blood, hemorheology, were neglected for at least another 80 years. In 1931, Fåhraeus and Lindqvist published their classic study entitled “The Viscosity of Blood in Narrow Capillary Tubes” [3] that re-awakened scientific interest in hemorheology. However, until fairly recently, progress in this branch of science has been relatively slow, primarily due to the absence of reliable hemorheological laboratory instruments.

Because of the non-Newtonian flow behavior of whole blood, viscosity measurements were initially limited to studies of plasma and serum. In fact, the clinical condition known as “Hyperviscosity Syndrome” was originally defined solely by high plasma viscosity. However, special instruments developed in the last few decades and dedicated to the measurement of various hemorheological parameters (e.g., whole blood viscosity, RBC aggregation, RBC deformability) greatly improve our measurement abilities and thus are a welcome addition to the early plasma viscometers.

In this chapter no comprehensive treatment of all described methods and techniques has been attempted. Rather, instead of listing all home-made techniques and instruments that have appeared in the literature and sometimes used only once by a single group, a survey of generally accepted methods and/or techniques as well as some recent developments are presented. Relevant website addresses are provided in the hope that these will be updated regularly by the manufacturers and vendors. However, in order to increase the direct practical value of this chapter, more detailed descriptions of relevant, commercially available instruments are given. Comparative studies of these methods and/or instruments are briefly discussed. Note that the latest version of the “Guidelines for Measurement of Blood Viscosity and Erythrocyte Deformability” [4] dates back to 1986 and a more recent version, comparing the newer techniques and instruments and giving generally agreed upon recommendations, is urgently needed. Finally, some general practical hemorheological laboratory techniques are described.