To investigate the flowability of a physiological fluid sample, an uptake passage (12) for the fluid sample (16), an actuator device (18) for the cyclic change in orientation of measuring particles (14) in the fluid sample (16), and a detector device (20, 22) for the preferably optical detection of the change in orientation of the measuring particles (14) are provided. In order to make reliable measurements possible with minimal instrument expense, it is proposed that the actuator device is formed by a pump unit (18) to produce a flow of the fluid sample (16) that travels back and forth along the uptake passage (12) and indicates the change in orientation of the measuring particles (14).