A viscometer suitable for rapid measurements in small volumes of highly viscous liquids is described. Using this device the viscometric affinity assay for glucose was studied under variable conditions in order to obtain basic information for the design of a viscometric glucose sensor. The viscosity of the dextran/Concanavalin A (ConA) solution is sensitive to glucose in a broad range of the shear stress. However, for measuring the glucose concentration with this sensitive liquid the strong dependence of the absolute viscosity on temperature and ConA concentration has to be taken into account. For the purpose of calibration a parameter more suitable than the absolute viscosity is the relative fluidity (F-r) that is defined by the actual measured viscosity at a given glucose concentration, the reference viscosity at a standard glucose concentration, and a constant linearization coefficient. F-r shows a linear dependence on the glucose concentration in the therapeutically interesting range up to 30 mM and is not significantly changed by moderate variations of the ConA concentration or temperature.